Capture Network Logs (NetLog) from Edge and Chrome (and Electron)

Problems in accessing websites can often be found and fixed if the network traffic between the browser and the website is captured as the problem occurs. This short post explains how to capture such logs.

Capturing Network Traffic Logs

If someone asked you to read this post, chances are good that you were asked to capture a web traffic log to track down a bug in a website or your web browser.

Fortunately, in Google Chrome or the new Microsoft Edge (version 76+), capturing traffic is simple:

  1. Optional but helpful: Close all browser tabs but one.
  2. Navigate the tab to chrome://net-export
  3. In the UI that appears, press the Start Logging to Disk button.
  4. Choose a filename to save the traffic to. Tip: Pick a location you can easily find later, like your Desktop.
  5. Reproduce the networking problem in a new tab. If you close or navigate the //net-export tab, the logging will stop automatically.
  6. After reproducing the problem, press the Stop Logging button.
  7. Share the Net-Export-Log.json file with whomever will be looking at it. Optional: If the resulting file is very large, you can compress it to a ZIP file.
Network Capture UI

Privacy-Impacting Options

In some cases, especially when you dealing with a problem in logging into a website, you may need to set either the Include cookies and credentials or Include raw bytes options before you click the Start Logging button.

Note that there are important security & privacy implications to selecting these options– if you do so, your capture file will almost certainly contain private data that would allow a bad actor to steal your accounts or perform other malicious actions. Share the capture only with a person you trust and do not post it on the Internet in a public forum.

Tutorial Video

If you’re more of a visual learner, here’s a short video demonstrating the traffic capture process.

In a followup post, I explore how developers can analyze captured traffic.


Appendix A: Capture on Startup

In rare cases, you may need to capture network data early (e.g. to capture proxy script downloads and the like. To do that, close Edge, then run:

msedge.exe --log-net-log=%USERPROFILE%\Desktop\ReproNetlog.json --net-log-capture-mode=Everything

If you want to capture unsanitized cookies and authentication headers, but not the response bodies, use --net-log-capture-mode=IncludeSensitive instead. Omit the final parameter entirely if you do not want to include the raw data and want just the “Strip Private Information” mode of capture.

Note: This approach also works for Electron JS applications like Microsoft Teams:

%LOCALAPPDATA%\Microsoft\Teams\current\Teams.exe --log-net-log=C:\temp\TeamsNetLog.json

Note: This will only capture the network traffic from the Chromium layer of Electron apps (e.g. web requests from the nodeJS side will not be captured) but it still may be very useful.

Appendix B: Limitations – No POST Data

One important shortcoming in the current NetLog file format is that it does not contain any request body data, even if you select the “Include Raw Bytes” option. If you need the request body data, you may need to collect a HTTP Archive (HAR) file instead.

  • Hit F12 to open the Developer Tools.
  • Activate the Network tab.
  • Ensure the recording button at the top of the tab is red
  • Tick the Preserve log checkbox.
  • Reproduce the problem
  • Right-click entries in the the grid and choose Save all as HAR with content
  • Share the HAR file only with a person you trust and do not post it on the Internet in a public forum.

Appendix C: References

Disabling TLS/1.0 and TLS/1.1 in the new Edge Browser

UPDATE: Timelines in this post were updated in March 2020 and October 2020 to reflect the best available information.

HTTPS traffic is encrypted and protected from snooping and modification by an underlying protocol called Transport Layer Security (TLS). Disabling outdated versions of the TLS security protocol will help move the web forward toward a more secure future. All major browsers (including Firefox, Chrome, Safari, Internet Explorer and Edge Legacy) have publicly committed to require TLS version 1.2 or later by default starting in 2020.

Starting in Edge 84, reaching stable in July 2020, the legacy TLS/1.0 and TLS/1.1 protocols will be disabled by default. These older protocol versions are less secure than the TLS/1.2 and TLS/1.3 protocols that are now widely supported by websites:

To help users and IT administrators discover sites that still only support legacy TLS versions, the edge://flags/#show-legacy-tls-warnings flag was introduced in Edge Canary version 81.0.392. Simply set the flag to Enabled and restart the browser for the change to take effect:

Subsequently, if you visit a site that requires TLS/1.0 or TLS/1.1, the lock icon will be replaced with a “Not Secure” warning in the address box, alongside the warning in the F12 Developer Tools Console:

As shown earlier in this post, almost all sites are already able to negotiate TLS/1.2. For those that aren’t, it’s typically either a simple configuration option in either the server’s registry or web server configuration file. (Note that you can leave TLS/1.0 and TLS/1.1 enabled on the server if you like, as browsers will negotiate the latest common protocol version).

In some cases, server software may have no support for TLS/1.2 and will need to be updated to a version with such support. However, we expect that these cases will be rare—the TLS/1.2 protocol is now over 11 years old.

Obsolete TLS Blocks Subdownloads

Often a website pulls in some page content (like script or images) from another server, which might be running a different TLS version. In cases where that content server does not support TLS/1.2 or later, the content will simply be missing from the parent page.

You can identify cases like this by watching for the message net::ERR_SSL_OBSOLETE_VERSION in the Developer Tools console:

Unfortunately, a shortcoming in this console notification means that it does not appear for blocked subframes; you’ll need to look in the Network Tab or a NetLog trace for such failures.

Group Policy Details

Organizations with internal sites that are not yet prepared for this change can configure group policies to re-enable the legacy TLS protocols.

For the new Edge, use the SSLVersionMin Group Policy. This policy will remain available until the removal of the TLS/1.0 and TLS/1.1 protocols from Chromium in May 2021. Stated another way, the new Edge will stop supporting TLS/1.0+1.1 (regardless of policy) in May 2021.

For IE11 and Edge Legacy, the policy in question is the (dubiously-named) “Turn off encryption support” found inside Windows Components/Internet Explorer/Internet Control Panel/Advanced Page. Edge Legacy and IE will likely continue to support enabling these protocols via GP until they are broken from a security POV; this isn’t expected to happen for a few years.

IE Mode Details

These older protocols will not be disabled in Internet Explorer and Edge Legacy until Spring 2021.

The New Edge has the ability to load administrator-configured sites in Internet Explorer Mode. IEMode tabs depend on the IE TLS settings, so if you need an IEMode site to load a TLS/1.0 website after Spring of 2021, you’ll need to enable TLS/1.0 using the “Turn off encryption support” group policy found inside Windows Components/Internet Explorer/Internet Control Panel/Advanced Page.

If you need to support a TLS/1.0 site in both Edge and IE Modes (e.g. the site is configured as “Neutral”), then you will need to set both policies (SSLVersionMin and “Turn off Encryption Support”).

Thanks for your help in securing the web!


WebOCs and HTTP/2

If you’ve built an application using the old Web Browser Control (mshtml, aka Internet Explorer), you might notice that by default it does not support HTTP/2. For instance, a trivial WebOC host loading Akamai’s HTTP2 test page:

When your program is running on any build of Windows 10, you can set a Feature Control Key with your process’ name to opt-in to using HTTP/2.

For applications running at the OS-native bitness, write the key here:


For 32-bit applications running on 64-bit Windows, write it here:
HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_WEBOC_ENABLE_HTTP2

Like so:

After you make this change and restart the application, it will use HTTP/2 if the server and network path supports it.

Using HTTP/2 should help improve performance and can even resolve functional bugs.


Update: Windows’ Internet Control Panel has a “HTTP2” checkbox, but it only controls web platform apps (IE and Legacy Edge), and unfortunately, the setting does not work properly for AppContainer/LowIL processes, which enable HTTP2 by default. This means that the checkbox, as of Windows 10 version 1909, is pretty much useless for its intended purpose (as only Intranet Zone sites outside of Protected Mode run at MediumIL).

A bug has been filed.

Update: Users of the new Chromium-based Edge browser can launch an instance with HTTP2 disabled using the disable-http2 command line argument, e.g. ms-edge.exe --disable-http2.

I’m not aware of a straightforward way to disable HTTP2 for the new Chromium-Edge-based WebView2 control, which has HTTP2 enabled by default.

The Pitfalls of EventSource over HTTP/1.1

While there are many different ways for servers to stream data to clients, the Server-sent Events / EventSource Interface is one of the simplest. Your code simply creates an EventSource and then subscribes to its onmessage callback:

Implementing the server side is almost as simple: your handler just prefaces each piece of data it wants to send to the client with the string data: and ends it with a double line-ending (\n\n). Easy peasy. You can see the API in action in this simple demo.

I’ve long been sad that we didn’t manage to get this API into Internet Explorer or the Legacy Edge browser. While many polyfills for the API exist, I was happy that we finally have EventSource in the new Edge.

Yay! \o/

Alas, I wouldn’t be writing this post if I hadn’t learned something new yesterday.

Last week, a customer reached out to complain that the new Edge and Chrome didn’t work well with their webmail application. After they used the webmail site for a some indeterminate amount time, they noticed that its performance slowed to a crawl– switching between messages would take tens of seconds or longer, and the problem reproduced regardless of the speed of the network. The only way to reliably resolve the problem was to either close the tabs they’d opened from the main app (e.g. the individual email messages could be opened in their own tabs) or to restart the browser entirely.

As the networking PM, I was called in to figure out what was going wrong over video conference. I instructed the user to open the F12 Developer Tools and we looked at the network console together. Each time the user clicked on a message, new requests were created and sat in the (pending) state for a long time, meaning that the requests were getting queued and weren’t even going to the network promptly.

But why? Diagnosing this remotely wasn’t going to be trivial, so I had the user generate a Network Export log that I could examine later.

In examining the log using the online viewer, the problem became immediately clear. On the Sockets tab, the webmail’s server showed 19 requests in the Pending state, and 6 Active connections to the server, none of which were idle. The fact that there were six connections strongly suggested that the server was using HTTP/1.1 rather than HTTP/2, and a quick look at the HTTP/2 tab confirmed it. Looking at the Events tab, we see five outstanding URLRequests to a URL that strongly suggests that it’s being used as an EventSource:

Each of these sockets is in the READING_RESPONSE state, and each has returned just ten bytes of body data to each EventSource. The web application is using one EventSource instance of the app, and the user has five tabs open to the app.

And now everything falls into place. Browsers limit themselves to 6 concurrent connections per server. When the server supports HTTP/2, browsers typically need just one connection because HTTP/2 supports multiplexing many (typically 100) streams onto a single connection. HTTP/1.1 doesn’t afford that luxury, so every long-lived connection used by a page decrements the available connections by one. So, for this user, all of their network traffic was going down a single HTTP/1.1 connection, and because HTTP/1.1 doesn’t allow multiplexing, it means that every action in the UI was blocked on a very narrow head-of-line-blocking pipe.

Looking in the Chrome bug tracker, we find this core problem (“SSE connections can starve other requests”) resolved “By Design” six years ago.

Now, I’m always skeptical when reading old bugs, because many issues are fixed over time, and it’s often the case that an old resolution is no longer accurate in the modern world. So I built a simple repro script for Meddler. The script returns one of four responses:

  • An HTML page that consumes an EventSource
  • An HTML page containing 15 frames pointed at the previous HTML page
  • An event source endpoint (text/event-stream)
  • A JPEG file (to test whether connection limits apply across both EventSources and other downloads)

And sure enough, when we load the page we see that only six frames are getting events from the EventSource, and the images that are supposed to load at the bottom of the frames never load at all:

Similarly, if we attempt to load the page in another tab, we find that it doesn’t even load, with a status message of “Waiting for available socket…”

The web app owners should definitely enable HTTP/2 on their server, which will make this problem disappear for almost all of their users.

However, even HTTP/2 is not a panacea, because the user might be behind a “break-and-inspect” proxy that downgrades connections to HTTP/1.1, or the browser might conceivably limit parallel requests on HTTP/2 connections for slow networks. As noted in the By Design issue, a server depending on EventSource in multiple tabs might use a BroadcastChannel or a SharedWorker to share a single EventSource connection with all of the tabs of the web application.

Alternatively, swapping an EventSource architecture with one based on WebSocket (even one that exposes itself as a EventSource polyfill) will also likely resolve the problem. That’s because, even if the client or server doesn’t support routing WebSockets over HTTP/2, the WebSockets-Per-Host limit is 255 in Chromium and 200 in Firefox.

Stay responsive out there!


AppOrWeb-to-WebApp Communication: Custom Scheme Handlers

I’ve previously written about Web-to-App communication via Application Protocols. App Protocols allow web content to invoke a native application outside of the browser.

WebApp advocates (like me!) want to continue to close the native/browser gaps that prevent web applications from becoming full-fledged replacements for native apps. To that end, I’ve recently spent some time looking at how the web platform allows JavaScript registration of a protocol handler, where the handling “app” is a same-origin web page.

Currently supported by Firefox and Chromium-based browsers (on platforms other than Android), the function navigator.registerProtocolHandler(scheme, url_template, description) enables a website to become a handler for a URL scheme.

Real-World Usage

The canonical use-case for this is web based email clients like Gmail. Gmail would like to be able to be the user’s handler for mailto links. When the user clicks a mailto link, the content of the link should be sent to a handler page on which responds accordingly (e.g. by creating a new email to the specified addressee).

The registerProtocolHandler API isn’t limited to the mailto scheme, however. It presently supports a short list of allowed schemes1, and any scheme named web+{one-or-more-lowercaseASCII}.

User Experience

I’ve built a page containing a number of test cases here. When you push the button to register a protocol handler, you receive a permission prompt from Chrome/Edge or Firefox:



To avoid annoying users, if the user declines Chrome’s prompt, the site is blocked from re-requesting permission to handle the protocol. A user must manually visit the settings page to unblock permission.

User-Gesture Requirements

If a page attempts to call registerProtocolHandler() on load or before the user has interacted with the page (a so called “gesture”), then Chromium-based browsers will not pop the permission prompt. Instead, an overlapping-diamonds icon is shown at the right-hand side of the address bar, with the text “This page wants to install a service handler.” Here’s what this looks like on Gmail:



Within Chrome, you can view your currently registered handlers (and sites blocked from asking to become the registered handler) by visiting chrome://settings/content/handlers.


Operating System Integration

One particularly interesting aspect of allowing web-based registration of protocol handlers is that it is desirable for the rest of the operating system outside of the browser to respect those protocol handler associations.

For example, clicking a mailto link in some other application should launch the browser to the web-based handler if registered. However, having the browser change system state in this manner is complicated, especially on modern versions of Windows whereby various protections have been put in place to try to prevent “hijacking” of file type and protocol handler associations.

Edge and Chrome will only attempt to become the systemwide handler for a protocol when running a channel that offers to become the default browser (e.g. Stable). On such a channel, if the browser wasn’t already the handler for the protocol, after the user clicks “Allow” on the Chrome permission bubble, a Windows UAC dialog is shown:


If the user accepts by clicking “Yes”, the RegisterChromeForProtocol function silently updates the registry:


Other Things I’ve Learned

  • Chrome, Edge, and Firefox disallow registration of protocol handlers in Private/Incognito/InPrivate modes.
  • With my patch landed, Chrome, Edge, and Firefox disallow registration of protocol handlers from non-secure contexts (e.g. HTTP). Due to the same-origin requirement for the handler URL, this effectively prevents the use of a non-secure page as a handler.
  • An upcoming patch proposes blocking registration from cross-origin subframes.
  • Chromium-based browsers enable IT admins to set default scheme-to-web mappings using Group Policy.
  • Chrome presently fails to enforce specified limits on web+ protocol names. Firefox does enforce the limits.
  • Firefox does not support targeting a RPH registered protocol as the target of a form POST request; it silently drops the POST body.
  • Firefox does not implement the unregisterProtocolHandler API. Users must manually unregister protocol handlers using the browser UI.
  • On Windows at least, neither Firefox Stable nor Firefox Nightly seems to try to become the systemwide handler for a scheme.
  • If you have a custom scheme link in a subframe, you probably want to add a target=_blank attribute on it. Otherwise, your protocol handler web page might navigate within that subframe and get blocked due to privacy settings or X-Frame-Options directives


1 The permitted schemes are bitcoin, geo, im, irc, ircs, magnet, mailto, mms, news, nntp, openpgp4fpr, sip, sms, smsto, ssh, tel, urn, webcal, wtai, xmpp.

Thoughts on DNS-over-HTTPS

Updated November 30, 2020 with new information about DoH in Edge, ECH, and HTTPSSVC records, and January 25, 2021 with a few remarks about Edge’s implementation.

Type in your web browser’s address bar and hit enter.

What happens?

Before connecting to the server, your browser must convert “” to the network address at which that server is located.


It does this lookup using a protocol called “DNS.” Today, most DNS transactions are conducted in plaintext (not encrypted) by sending UDP messages to the DNS resolver your computer is configured to use.

There are a number of problems with the 36-year-old DNS protocol, but a key one is that the unencrypted use of UDP traffic means that network intermediaries can see (and potentially modify) your lookups, such that attackers can know where you’re browsing, and potentially even direct your traffic to some other server.

The DNS-over-HTTPS (DoH) protocol attempts to address some of these problems by sending DNS traffic over a HTTPS connection to the DNS resolver. The encryption (TLS/QUIC) of the connection helps prevent network intermediaries from knowing what addresses your browser is looking up– your queries are private between your PC and the DNS resolver that is providing the answers. The expressiveness of HTTP (with request and response headers) provides interesting options for future extensibility, and the modern HTTP2 and HTTP3 protocols aim to provide high-performance and parallel transactions with a single connection.

An additional benefit of using securing DNS is that it enables the safe introduction of new security-related features to the DNS. That capability can help secure all forms of traffic, not just the target IP addresses. For instance, the proposed HTTPSSVC record will allow clients to securely receive useful information which can improve the security and performance of the HTTP2/HTTP3 connections used to download web pages.

Try It

Support for DNS-over-HTTPS is coming to many browsers and operating systems (including a future version of Windows). You can even try DoH out in the newest version of Microsoft Edge (v79+) by starting the browser with a special command line flag. The following command line will start the browser and instruct it to perform DNS lookups using the Cloudflare DoH server:

msedge.exe --enable-features="DnsOverHttps<DoHTrial" --force-fieldtrials="DoHTrial/Group1" --force-fieldtrial-params="DoHTrial.Group1:Fallback/false/Templates/"

You can test to see whether the feature is working as expected by visiting Unfortunately, this command line flag presently only works on unmanaged PCs, meaning it doesn’t do anything from PCs that are joined to a Windows domain.

Microsoft Edge Fall 2020 Update 

Starting in Edge 86, DNS-over-HTTPS configuration is now available inside edge://settings/privacy. Users may either leave the default at Use current service provider (in which case DoH will only be used if the user’s OS DNS provider is known to support DoH) or they may explicitly configure a DoH provider. Explicit configuration allows selection from a small set of popular DoH providers, or a fully-qualified HTTPS URL to the DoH provider may be entered in the text box.

DoH Consumer

Notably, for Enterprise/Managed PCs, the Edge Settings UI is disabled– only administrators may configure the settings using two related Group Policies. 

DoH Enterprise

A few remarks about Edge’s implementation:

  • If your OS-configured DNS provider is on a list known to support DoH, we try to start speaking DoH. If it fails, we fall back to non-secure DNS.
  • If you manually pick a DoH provider from the Settings Page’s list, we use that. There are only a few, and there’s no difference based on locale. If it fails, we do NOT fall back.
  • If you manually enter a DoH URL in the Settings page, you can use whatever provider you want. If it fails, we do NOT fall back.
  • If you’re an Enterprise User, there’s no end-user UI and everything is configured (URL, whether fallback is allowed) exclusively by two related Group Policies.
  • Unlike Firefox, we do not have any code to try to advertise/encourage the user to pick a DoH provider.
  • Long term, everyone is working on approaches whereby a DNS provider can “advertise” support for DoH rather than being added to a list in Chromium, but we’re probably many months away from anything happening there.
  • Secure DNS in the Edge Privacy Whitepaper

Some Thoughts, In No Particular Order

Long-time readers of this blog know that I want to “HTTPS ALL THE THINGS” and DNS is no exception. Unfortunately, as with most protocol transitions, this turns out to be very very complicated.


The privacy benefits of DNS-over-HTTPS are predicated on the idea that a network observer, blinded from your DNS lookups by encryption, will not be able to see where you’re browsing.

Unfortunately, network observers, by definition, can observe your traffic, even if the traffic encrypted.

The network observer will still see the IP addresses you’re connecting to, and that’s often sufficient to know what sites you’re browsing.

Worse, they are usually still able to tell what specific HTTPS site you’re visiting on that IP address. That’s because one of the current limitations of HTTPS is that the browser sends, in unencrypted form a Server Name Indication (SNI), the hostname it expects to see in the server’s certificate as a part of the ClientHello HTTPS handshake message. Closing the “SNI leak” requires implementation of Encrypted Client Hello [Explainer] (previously Encrypted SNI (ESNI)) and this feature is not yet implemented in Chromium.

Privacy From Observers, Not the Resolver

If your Internet Service Provider (say, for example, Comcast) is configured to offer DNS-over-HTTPS, and your browser uses their resolver, your network lookups are protected from observers on the local network, but not from the Comcast resolver.

Because the data handling practices of resolvers are often opaque, and because there are business incentives for resolvers to make use of lookup data (for advertising targeting or analytics revenue), it could be the case that the very actor you are trying to hide your traffic from (e.g. your ISP) is exactly the one holding the encryption key you’re using to encrypt the lookup traffic.

To address this, some users choose to send their traffic not to the default resolver their device is configured to use (typically provided by the ISP) but instead send the lookups to a “Public Resolver” provided by a third-party with a stronger privacy promise.

However, this introduces its own complexities.

Public Resolvers Don’t Know Private Addresses

A key problem in the deployment of DNS-over-HTTPS is that public resolvers (Google Public DNS, Cloudflare, Open DNS, etc) cannot know the addresses of servers that are within an intranet. If your browser attempts to look up a hostname on your intranet (say using the public resolver, the public resolver not only gets information about your internal network (e.g. now Google knows that you have a server called MySecretServer.intranet) but it also returns “Sorry, never heard of it.” At this point, your browser has to decide what to do next. It might fail entirely (“Sorry, site not found”) or it might “Fail open” and perform a plain UDP lookup using the system-configured resolver provided by e.g. your corporate network administrator.

This fallback means that a network attacker might simply block your DoH traffic such that you perform all of your queries in unprotected fashion. Not great.

Even alerting the user to such a problem is tricky: What could the browser even say that a human might understand? “Nerdy McNerdy Nerd Nerd Nerd Nerd Nerd Address Nerd Resolution Nerd Geek. Privacy. Network. Nerdery. Geekery. Continue?”

Centralization Isn’t Great

Centralizing DNS resolutions to the (relatively small) set of public DNS providers is contentious, at best. Some European jurisdictions are uncomfortable about the idea that their citizens’ DNS lookups might be sent to an American tech giant.

Some privacy-focused users are primarily worried about the internet giants (e.g. Google, Cloudflare) and are very nervous that the rise of DoH will result in browsers sending traffic to these resolvers by default. Google has said they won’t do that in Chrome, while Firefox is experimenting with using Cloudflare by default in some locales.

Content Filtering

Historically, DNS resolutions were a convenient choke point for schools, corporations, and parents to implement content filtering policies. By interfering with DNS lookups for sites that network users are forbidden to visit (e.g adult content, sites that put the user’s security at risk, or sites that might result in legal liability for the organization), these organizations were able to easily prevent non-savvy users from connecting to unwanted sites. Using DoH to a Public DNS provider bypasses these types of content filters, leaving the organization with unappealing choices: start using lower-granularity network interception (e.g. blocking by IP addresses), installing content-filters on the user’s devices directly, or attempting to block DoH resolvers entirely and forcing the user’s devices to fall back to the filtered resolver.

Geo CDNs and Other Tricks

In the past, DNS was one mechanism that a geographically distributed CDN could use to load-balance its traffic such that users get the “best” answers for their current locale. For instance, if the resolver was answering a query from a user in Australia, it might return a different server address than when resolving a query from a user in Florida.

These schemes and others get more complicated when the user isn’t using a local DNS resolver and is instead using a central public resolver, possibly provided by a competitor to the sites that the user is trying to visit.

Don’t Despair

Despite these challenges and others, DNS-over-HTTPS represents an improvement over the status quo, and as browser and OS engineering teams and standards bodies invest in addressing these problems, we can expect that deployment and use of DoH will grow more common in the coming years.

DoH will eventually be a part of a more private and secure web.

-Eric Lawrence

bye: FTP Support Is Going Away

Support for the venerable FTP protocol is being removed from Chromium. Standardized in 1971, FTP is not a safe protocol for the modern internet. Its primary defect is lack of support for encryption (FTPS isn’t supported by any popular browsers), although poor support for authentication and other important features (download resumption, proxying) also have hampered the protocol over the years.

With removal first proposed by the networking lead nearly six years ago, FTP support has been gradually pared back, first blocking such urls for subresources in Chrome 59, and later forcing FTP resources to be treated as downloads in Chrome 72. Now FTP support be going away entirely, starting in version 80, although a flag (chrome://flags/#enable-ftp) will remain available to turn it back on for a limited time.

After FTP support is removed, clicking on a FTP link will either launch the operating system’s registered FTP handler (if any), or will silently fail to do anything (as Chrome fails silently when an application protocol handler is not installed).

If your scenario depends on FTP today, please switch over to HTTPS as soon as possible.




Improving Privacy by Limiting Referrers

Updated July 31, 2020 to reflect changes planned to ship in Chrome 85 and Edge 86.

As your browser navigates from page to page, servers are informed of the URL from where you’ve come from using the Referer HTTP header1; the document.referrer DOM property reveals the same information to JavaScript.

Similarly, as the browser downloads the resources (images, styles, JavaScript) within webpages, the Referer header on the request allows the resource’s server to determine which page is requesting the resource.

The Referrer is omitted in some cases, including:

  • When the user navigates via some mechanism other than a link in the page (e.g. choosing a bookmark or using the address box)
  • When navigating from HTTPS pages to HTTP pages
  • When navigating from a resource served by a protocol other than HTTP(S)
  • When the page opts-out (details in a moment)


The Referrer mechanism can be very useful, because it helps a site owner understand from where their traffic is originating. For instance, WordPress automatically generates this dashboard which shows me where my blog gets its visitors:


I can see not only which Search Engines send me the most users, but also which specific posts on Reddit are driving traffic my way.

Privacy Implications

Unfortunately, this default behavior has a significant impact on privacy, because it can potentially leak private and important information.

Imagine, for example, that you’re reviewing a document your mergers and acquisitions department has authored, with the URL​Q4/PotentialAcquisitionTargetsUpTo5M.docx. Within that document, there might have a link to​/financialdisclosures.htm. If you were to click that link, the navigation request to Fabrikam’s server will contain the full URL of the document that led you there, potentially revealing information that your firm would’ve preferred to keep quiet.

Similarly, your search queries might contain something you don’t mind Bing knowing (“Am I required to disclose a disease before signing up for”) but that you didn’t want to immediately reveal to the site where you’re looking for answers.

If your web-based email reader puts your email address in the URL, or includes the subject of the current email, links you click in that email might be leaking information you wish to keep private.

The list goes on and on. This class of threat was noted almost thirty years ago:

Referrer Policy

Websites have always had ways to avoid leaking information to navigation targets, usually involving nonstandard navigation mechanisms (e.g. meta refresh) or by wrapping all links so that they go through an innocuous page (e.g.

However, these mechanisms were non-standard, cumbersome, and would not control the referrer information sent when downloading resources embedded in pages. To address these limitations, Referrer Policy was developed and implemented by most browsers2.


Referrer Policy allows a website to control what information is sent in Referer headers and exposed to the document.referrer property. As noted in the spec, the policy can be specified in several ways:

  • Via the Referrer-Policy HTTP response header.
  • Via a meta element with a name of referrer.
  • Via a referrerpolicy content attribute on an aareaimgiframe, or link element.
  • Via the noreferrer link relation on an aarea, or link element.
  • Implicitly, via inheritance.

The policy can be any of the following:

  • no-referrer – Do not send a Referer.
  • unsafe-url – Send the full URL (lacking only auth info and fragment), even on navigations from HTTPS to HTTP.
  • no-referrer-when-downgrade – Don’t send the Referer when navigating from HTTPS to HTTP. [The longstanding default behavior of browsers.]
  • strict-origin-when-cross-origin – For a same-origin navigation, send the URL. For a cross-origin navigation, send only the Origin of the referring page. Send nothing when navigating from HTTPS to HTTP. [Spoiler alert: The new default.]
  • origin-when-cross-origin For a same-origin navigation, send the URL. For a cross-origin navigation, send only the Origin of the referring page. Send the Referer even when navigating from HTTPS to HTTP.
  • same-origin – Send the Referer only for same-origin navigations.
  • origin – Send only the Origin of the referring page.
  • strict-origin – Send only the Origin of the referring page; send nothing when navigating from HTTPS to HTTP.
  • empty string – Inherit, or use the default

As you can see, there are quite a few policies. That’s partly due to the strict- variations which prevent leaking even the origin information on HTTPS->HTTP navigations.

Improving Defaults

With this background out of the way, the Chromium team has announced that they plan to change the default Referrer Policy from no-referrer-when-downgrade to strict-origin-when-cross-origin. This means that cross-origin navigations will no longer reveal path or query string information, significantly reducing the possibility of unexpected leaks.

As with other big privacy changes, this change is slated to ship in v80 (Update: Later delayed to Chrome 85 and Edge 86), the code has been in for five years and you can enable it in Chrome 78+ and Edge 78+:

  1. Visit chrome://flags/#reduced-referrer-granularity
  2. Set the feature to Enabled
  3. Restart your browser

I’ve published a few toy test cases for playing with Referrer Policy here.

As noted in their Intent To Implement, the Chrome team are not the first to make changes here. As of Firefox 70 (Oct 2019), the default referrer policy is set to strict-origin-when-cross-origin, but only for requests to known-tracking domains, OR while in Private mode. In Safari ITP, all cross-site HTTP referrers and all cross-site document.referrers are downgraded to origin. Brave forges the Referer (sending the Origin of the target, not the source) when loading 3rd party resources.

Understand the Limits

Note that this new default is “opt-out”– a page can still choose to send unrestricted referral URLs if it chooses. To opt-out, a site can set a ReferrerPolicy for the entire document using the META tag or HTTP header, or can opt-out a single link with the ReferrerPolicy attribute on the element:

<a referrerpolicy="unsafe-url" href="">Send the full unstripped Referrer, even to HTTP sites</a>

As an author, I selfishly hope that sites like Reddit and Hacker News might do so.

Also note that this new default does not in any way limit JavaScript’s access to the current page‘s URL. If your page at includes a tracking script:


… the HTTPS request for track.js will send Referer:, but when the script runs, it will have access to the full URL of its execution context ( via the window.location.href property.

Test Your Sites

If you’re a web developer, you should test your sites in this new configuration and update them if anything is unexpectedly broken. If you want the browser to behave as it used to, you can use any of the policy-specification mechanisms to request no-referrer-when-downgrade behavior for either an entire page or individual links.

Or, you might pick an even stricter policy (e.g. same-origin) if you want to prevent even the origin information from leaking out on a cross-site basis. You might consider using this on your Intranet, for instance, to help prevent the hostnames of your Intranet servers from being sent out to public Internet sites.

You can read more about this topic in the Chrome team’s documentation.

Stay private out there!


1 The misspelling of the HTTP header name is a historical error which was never corrected.

2 Notably, Safari, IE11, and versions of Edge 18 and below only supported an older draft of the Referrer policy spec, with tokens never (matching no-referrer), always (matching unsafe-url), origin (unchanged) and default (matching no-referrer-when-downgrade). Edge 18 supported origin-when-cross-origin, but only for resource subdownloads.

Restrictions on File Urls

For security reasons, Edge 76+ and Chrome impose a number of restrictions on file:// URLs, including forbidding navigation to file:// URLs from non-file:// URLs.

If a browser user clicks on a file:// link on an https-delivered webpage, nothing visibly happens. If you open the the Developer Tools console, you’ll see a note: “Not allowed to load local resource: file://host/whatever”.

In contrast, Edge18 (like Internet Explorer before it) allowed pages in your Intranet Zone to navigate to URLs that use the file:// url protocol; only pages in the Internet Zone were blocked from such navigations1.

No option to disable this navigation blocking is available in Chrome or Edge 76+.

What’s the Risk?

The most obvious problem is that the way file:// retrieves content can result in privacy and security problems. Pulling remote resources over file:// can leak your user account information and a hash of your password to the remote site. What makes this extra horrific is that if you log into Windows using an MSA account, the bad guy gets both your global userinfo AND a hash he can try to crack.

Beyond the data leakage risks related to remote file retrieval, other vulnerabilities related to opening local files also exist. Navigating to a local file might result in that file opening in a handler application in a dangerous or unexpected way. The Same Origin Policy for file URLs is poorly defined and inconsistent across browsers, which can result in security problems.

Workaround: IE Mode

Enterprise administrators can configure sites that must navigate to file:// urls to open in IE mode. Like legacy IE itself, IE mode pages in the Intranet zone can navigate to file urls.

Workaround: Extensions

Unfortunately, the extension API chrome.webNavigation.onBeforeNavigate does not fire for file:// links that are blocked in HTTP/HTTPS pages, which makes working around this blocking this via an extension difficult.

One could write an extension that uses a Content Script to rewrite all file:// hyperlinks to an Application Protocol handler (e.g. file-after-prompt://) that will launch a confirmation dialog before opening the targeted URL via ShellExecute or explorer /select,”file://whatever”, but this would entail rewriting the extension rewriting every page which has non-zero performance implications. It also wouldn’t fix up any non-link file navigations (e.g. JavaScript that calls window.location.href=”file://whatever”).

Similarly, the Enable Local File Links extension simply adds a click event listener to every page loaded in the browser. If the listener observes the user clicking on a link to a file:// URL, it cancels the click and directs the extension’s background page to perform the navigation to the target URL, bypassing the security restriction by using the extension’s (privileged) ability to navigate to file URLs. But this extension will not help if the page attempts to use JavaScript to navigate to a file URI, and it exposes you to the security risks described above.

Necessary but not sufficient

Unfortunately, blocking file:// urls in the browser is a good start, but it’s not complete. There are myriad formats which have the ability to hit the network for file URIs, ranging from Office documents, to emails, to media files, to PDF, MHT, SCF files, etc, and most of them will do so without confirmation. Raymond Chen explores this in Subtle ways your program can be Internet-facing.

In an enterprise, the expectation is that the Organization will block outbound SMB at the firewall. When I was working for Chrome and reported this issue to Google’s internal security department, they assured me that this is what they did. I then proved that they were not, in fact, correctly blocking outbound SMB for all employees, and they spun up a response team to go fix their broken firewall rules. In a home environment, the user’s router may or may not block the outbound request.

Various policies are available, but I get the sense that they’re not broadly used.

Navigation Restrictions Aren’t All…

This post mostly covers navigating to file:// URLs, but another question which occasionally comes up is “how can I embed a subresource like an image or a script from a file:// URL into my HTTPS-served page.” This, you also cannot do, for similar security/privacy reasons. And that’s probably a good thing.

Chromium allows HTML pages served from file:// URIs to load images and scripts from the same path, but Legacy Edge (v18) and Internet Explorer are the only browsers that consider all local-PC file:// URIs to be same-origin, allowing such pages to refer to other HTML resources on the local computer. Other browsers treat file origins as unique, blocking DOM interactions between frames from different local files, etc.

Chromium’s Same-Origin-Policy treats file: URLs as unique origins, which means that if you open an XML file from a file: URL, any XSL referenced by the XML is not permitted to load and the page usually appears blank, with the only text in the Console ('file:' URLs are treated as unique security origins.) noting the source of the problem.

This behavior impacts scenarios like trying to open Visual Studio Activity Log XML files and the like. To workaround the limitation, you can either embed your XSL in the XML file as a data URL:

…or you can launch Microsoft Edge or Chrome using a command line argument that allows such access:

msedge.exe --allow-file-access-from-files

However, please note that this flag doesn’t remove all restrictions on file, and only applies to pages served from file origins.

Consider a page loaded from a file on disk that contains three IFRAMEs to text files (one in the same folder, one in a sub folder, and one in a different folder altogether), three fetch() requests for the same URLs, and three XmlHttpRequests for the same URLs. By default, in Chromium, all three IFRAMEs load; in Firefox, only the first two load.

However, all of the fetch and XHR calls are blocked in both browsers:

If we relaunch Chromium with the --allow-file-access-from-files argument, we see that the fetch() calls all continue to fail, but the XHRs succeed:

In Firefox, setting privacy.file_unique_origin to false allows both fetch and XHR to succeed for the text file in the same folder and the subfolder, but the text file in the unrelated folder remains forbidden.


1 Interestingly, some alarmist researchers didn’t realize that file access was allowed only on a per-zone basis, and asserted that IE/Edge would directly leak your credentials from any Internet web page. This is not correct. It is further incorrect in old Edge (Spartan) because Internet-zone web pages run in Internet AppContainers, which lack the Enterprise Authentication permission, which means that they don’t even have your credentials.

Same-Site Cookies By Default

The Chrome team is embarking on a clever and bold plan to change the recipe for cookies. It’s one of the most consequential changes to the web platform in almost a decade, but with any luck, users won’t notice anything has changed.

But if you’re a web developer, you should start testing your sites and services now to help ensure a smooth transition.

What’s this all about?

As originally designed, cookies were very simple. When a browser made a request to a website, that website could return a tiny piece of text, called a cookie, to the browser. When the web browser subsequently requested any resource from that website, the cookie string would be echoed back to the server that first sent it.

Simple, right?

A bit too simple, as it turns out.

Browser designers have spent the last two decades trying to clear up the mess that this one simple feature causes, and alternatives might never gain adoption.

There are two major classes of problem with the design of cookies: Privacy, and Security.


The top privacy problem is that cookies are sent every time a request is made for a resource, even if that request is made from a completely different context. So, if you visit, that page might request a tracking pixel from This tracking pixel might set a cookie. The tracking pixel’s cookie is called a third party cookie because it was set by a domain unrelated to the page itself.

If you later visit, which also contains a tracking pixel from, the tracking pixel’s cookie set on your visit to is sent to, and now that tracker knows that you’ve visited both sites. As you browse more and more sites that contain a tracking pixel from the same provider, that provider can build up a very complete profile of the sites you like to visit, and use that information to target ads to you, sell the data to a data aggregation company, etc.

Today, Brave blocks 3rd party cookies by default, while Safari’s ITP feature does something more intricate. Firefox and the new Edge have “Tracking Prevention” features that block 3rd-party cookies from known trackers.

Most browsers offer a setting to turn off ALL third party cookies, and older versions of Internet Explorer used to P3P block cookies that did not promise to abide by reasonable privacy protections. However, almost all users leave 3rd party cookies enabled, and enough sites sent fraudulent P3P declarations that the P3P support was ripped out of the only browser that supported it.


The security problems with cookies are a bit more subtle.

In most cases, after you log in, a site will store your identity in a cookie, such that you don’t have to reenter your password on every page, or retap your security key every time you do anything. An authentication token is stored in a cookie, and each request you make to a site carries that cookie and token.

The problem is that this creates the possibility of a cross site request forgery attack, in which an attacker carefully crafts a request to a website to which you are logged in. When you visit the attacker’s site (say, to read a news article or view an image link posted to your social media feed), the attacker’s page instructs your browser to send its malicious request (“Transfer $1000 from me to @badguy”) to the victim site where you are logged in (e.g. https://bank.example).

Normally, such a request would be ignored or responded to by a demand for credentials, but because your browser is already logged in to bank.example and because your browser made the request, the server receives the cookie containing your authentication token and deems the request legitimate. You’ve been robbed! This class of attack is called the confused deputy attack.

Now, there are myriad ways to protect against this problem, but they all require careful work on the part of web application developers, and a long history of exploits shows that failing to protect against CSRF is a common mistake.

Other Privacy and Security Problems

I’ve described the biggest and most prominent of the security and privacy problems with the design of cookies, but those are just the tip of the iceberg. There are many other problems, including:

  • Because cookies are sent on plaintext HTTP requests, a passive network observer can watch your cookies as they’re sent over the network and correlate requests back to a single client. The NSA famously abused this vulnerability.
  • Cookies are sent to servers which respond with data that might allow Cross Site Leaks or violations of Same Origin Policy. For instance, an attacker might include in their page several guesses as to your identity. If they guess right (e.g. your cookie matches the URL identity), the images loads and now the attacker site knows exactly who you are:
  • Cookies can be trivially stolen in a XSS Attack if the HTTPOnly attribute was not set.
  • Cookies can be trivially leaked if the server forget to set the Secure attribute and the site isn’t on the HSTS preload list.
  • Same Origin Policy blocks reading of cross-origin resources, but this depends on the integrity of the browser sandbox. Attacks like Spectre weaken this guarantee. Ambient authentication (like cross-origin cookies) weakens Cross-Origin-Read-Blocking‘s ability to prevent a compromised renderer from stealing data.

Cookie Design Improvements

Over the years, browsers have introduced more and more features and toggles to help lock down cookies, from the Secure and HTTPOnly attributes to Cookie Prefixes (nee Magic Named Cookies).

Perhaps the most promising improvement is a feature called SameSite cookies, by which cookies can opt-in to being sent only in a first-party context:

Set-Cookie: __HostAuth=F123ABCA; SameSite=Strict; secure; httponly;

This helps protect your site against CSRF attacks and helps mitigate leakage of the user’s identity in a cross-site context.

There’s a nice SameSite cookie explainer (with pictures!).

While broadly supported by browsers, the SameSite directive isn’t getting used everywhere it should be.

Big Changes are Coming!

So the Chrome folks plan to change that.

In Chrome 85 (and Edge 86) and later, cookies will default to SameSite=Lax. This means that cookies will automatically be sent only in a first party context unless they opt-out by explicitly setting a directive of None:

Set-Cookie: ACookieAvailableCrossSite; SameSite=None; secure; httponly

This change is small in size, and huge in scope. It has huge implications for any site that expects its cookies to be used in a cross-origin context.

What’s the Immediate Good?

In one fell swoop, many websites will get more secure. Sites that were previously vulnerable to CSRF and cross-site leak attacks will be protected from attack in the most popular browser.

Privacy improves, because setting and sending of 3rd party cookies are blocked-by-default:


Who’s on board?

We plan to match this change in default for the new Edge browser (with experiments starting in v82 and shipping in Edge 86 Stable). However, there’s no plan to match this change for Internet Explorer (please stop using it!) or the old Edge (v18 and earlier).

Per Chromium’s Intent-to-Implement announcement, Firefox is looking into matching the change, although they’ve joking-not-joking suggested that they’re going to let Chrome lead the charge (and bear the brunt of the compatibility impact) before turning the feature on by default.

Per the I2I, Safari has not yet weighed in on this change. Safari’s ITP feature already imposes many interesting restrictions on cross-site cookies.

What Can Go Wrong?

If users visit a site that expects its cookies to be available but the cookies are missing, users might get a confusing error message suggesting that they toggle a setting that won’t help:


Or, the site might just redirect between its identity provider and itself forever.

These sorts of problems happen on sites that use Federated Identity providers that depend on accessing cookies from 3rd-party subframes:


To fix this, the identity provider site will either need to set SameSite=None on its cookies, or will need to use a browser storage feature (e.g. localStorage) that is not impacted by this change. Please note that other browser features do impact the availability of DOM Storage, so it’s not a silver bullet.

Rollout Plan

UPDATE: After assorted delays and experiments, Chrome is shipping this change on-by-default in 85, and Edge is shipping it in Edge 86.

The Chrome team has set an ambitious timeline which calls for turning this feature on-by-default for Chrome 80, slated for stable release onFebruary 4th, 2020. Chrome’s rollout plan includes enabling the new default on an experimental basis in Chrome 79 pre-release [Beta/Dev/Stable] channels for machines which are not externally managed — attempting to defer walking into the compatibility minefield of enterprise intranets. Presently, this exclusion does not apply to machines that are domain-joined via AAD due to a limitation in Chromium.

The Chrome team also announced two enterprise policies for Chrome 80+ that will allow admins to opt-out of the new default entirely, or to opt-out only specific sites. Edge expects to offer these same policies.

Developer Tooling

Developers who wish to enable the SameSite-by-Default feature locally for testing purposes can do so by visiting chrome://flags and searching for SameSite:


Set the SameSite by default cookies feature to Enabled and restart the browser.

You can view the cookies used by the current page using the Application tab of the Developer Tools; the column at the far right shows the declared SameSite attribute:


The Chrome team have enabled logging in the Developer Tools to notify web developers that cookie behavior is changing. Visit chrome://flags/cookie-deprecation-messages to ensure that the warnings are enabled:


If you then explore my test page, you can see the notices from the tools:


The Cookies subtab of the Network tab picked up a new checkbox “show filtered out request cookies” which allows you to see (in yellow) which cookies were not sent for the selected request due to SameSite rules:


Cookies restricted by SameSite rules are also logged in NetLog captures (issue 1005217).

Problems and Accommodations

While the vast majority of cookie scenarios will continue to work as expected, compatibility breaks are inevitable. Unfortunately, some of these breaks might not be trivially fixed by adding the SameSite=None attribute.

For instance, older versions of Safari treated SameSite=None as SameSite=Strict, which means that servers must avoid sending the None token to Safari 12.

The .NET Framework’s cookie writer used to simply omit the SameSite attribute when the SameSiteMode was “None.” Changing this will require the affected sites to update their framework to a version with the patch.

Early in our investigations, we found another problem related to how SameSite impacts cookies sent while navigating.

Specifically, over a million sites first set an anti-CSRF cookie on themselves, then redirect to a federated Login provider, then the Login provider POSTs the login information back to the site. That initial anti-CSRF cookie is only meant to be used in a first party context. Crucially, however, SameSite cookies are not sent on navigations if the navigations use the HTTP POST verb. Making the anti-CSRF cookies SameSite=Lax by default breaks this scenario and thus breaks tons of websites.


The Two Minute Mitigation

Demanding these security cookies be set to SameSite=None would be both onerous (many more sites would need to change) and misleading (because these cookies are really only meant to go to a 1st party context).

To address this breakage, the new default was adjusted to allow a SameSite-Lax-by-Default cookie to be sent on a subsequent POST requests for two minutes, significantly reducing the breakage without giving up all of the security benefit of the change.

Note that the 2 minute mitigation might not be enough for login scenarios that take longer than 2 minutes. For instance, consider the case where the login flow is happening in a background tab, or you have to fetch your Security Key, or a child must get a parent’s permission, etc. Sites that wish to handle scenarios like this will need to store a copy of their anti-CSRF token elsewhere (e.g. sessionStorage seems appropriate).

The Chrome team plans to eventually remove the 2 minute mitigation entirely.

Compat Landmine: document.cookie

In Firefox and Safari, the document.cookie DOM property matches the Cookie header, including omission of cookies that were restricted by SameSite navigation rules.

In contrast, in Chrome and Edge, SameSite cookies that are omitted from the Cookie header are still included in the document.cookie collection following a cross-origin navigation. I’ve been convinced that this actually makes more sense, although the reasoning is subtle [issue].

To the extent possible, you should set your cookies with the httponly attribute, so that they’re not available to JavaScript and this compatibility difference is irrelevant.

Test Steps

To test this change in Microsoft Edge, set:

  1. edge://flags/#same-site-by-default-cookies to ENABLE
  2. edge://flags/#cookies-without-same-site-must-be-secure to ENABLE
  3. Close all instances of the browser and start it using msedge.exe –enable-features=SameSiteDefaultChecksMethodRigorously

Step #3 disables the two-minute mitigation that allows SameSiteByDefault cookies on POST for two minutes; this exemption is slated for removal from Chromium at some unknown time (likely 6-12 months).

Overall testing guidance from Chromium applies to Edge:

If you’re a Fiddler user, you can use this script to easily visualize which cookies are being set with which SameSite values.

What’s Next?

After this change lands, users get more security and more privacy. But that’s just the start.

The next step is to combat the “non-secure-cookies-are-trackable” attack mentioned previously. To prevent non-secure cross-site cookies being used by network observers to follow users around the web, SameSite=None cookies will be blocked if set without the Secure attribute. Chrome’s timeline for enabling this change by default seems squishier, but ChromeStatus claims it is also slated for Chrome 80. Update: The SameSiteNoneMustBeSecure change is launching in parallel with SameSiteLaxByDefault for both Chrome and Edge.

After that, the next step is to combat the inevitable abuse by trackers.

Because trackers can simply opt their own cookies out of restrictions by setting SameSite=None, trackers will do so. But this isn’t is bad as you think– by forcing sites to explicitly declare each cookie for which cross-site use is intended, browsers can then focus extra love and attention around such cookies.

If we peek at Chrome’s flags page today, we see an interesting hint about the Chrome team’s plans:


Enabling that option enables EnableRemovingAllThirdPartyCookies which adds a new Remove Third-Party Cookies button to the All cookies and site data page. When clicked, it pops the following dialog:Delete3rdPartyButton

The HandleRemoveThirdParty() function invoked by the Clear button clears not only the cookies from those domains, but also all of the site data for the sites on which those cookies existed. This provides a strong disincentive for sites to opt-in to SameSite=None cookies unless they really need to.

(Disclaimer: Chrome might never launch the “Clear third-party cookies” button, but it’s in the code today).

You can expect that browser designers will soon dream up new and interesting remediations for cookies marked for access across multiple sites. For instance, browsers could limit the lifetime of those cookies to days or hours, or even a single browser session (tricky).

We live in interesting times!

Update: Chrome pushed back experimenting with this feature from Chrome 78 to Chrome 79. As of August 2020, they’ve enabled the feature for all Chrome 80+ users in all channels.

Update: The Chromium team have published a post about the new SameSite cookie default on their blog, including a list of incompatible legacy browsers that refuse to accept cookies that specify SameSite=None, and guidance on their rollout timeline. They also provide a Simple Test Page to see how your browser behaves.


Cookie-dough hero photo atop this post by Pam Menegakis on Unsplash.