Seek and Destroy Non-Secure References Using the moarTLS Analyzer

tl;dr: I made a Chrome Extension that finds security vulnerabilities.
It’s now available for Firefox too!

To secure web connections, TLS-enabling servers is only half the battle; the other half is ensuring that TLS is used everywhere.

Unfortunately, many HTTPS sites today include insecure references that provide an network-based attacker the opportunity to break into the user’s experience as they interact with otherwise secure sites. For instance, consider the homepage of Fidelity Investments:

Fidelity Homepage

You can see that the site has got the green lock and it’s using an EV certificate such that the organization’s name and location are displayed. Looks great! Even if you loaded this page over a coffee shop’s WiFi network, you’d feel pretty good about interacting with it, right?

Unfortunately, there’s a problem. Hit F12 to open the Chrome Developer Tools, and use the tool to select the “Open An Account” link in the site’s toolbar. That’s the link you’d click to start giving the site all of your personal information.

href attribute containing HTTP

Oops. See that http:// hiding out there? Even though Fidelity delivered the entire homepage securely, if a user clicks that link, a bad guy on the network has the opportunity to supply his own page in response! He can either return a HTML response that asks the victim for their information, or even redirect to a phony server (e.g. so that a lock icon remains in the address bar.

Adding insult to injury, what happens if a bad guy doesn’t take advantage of this hole?

    301 Redirect to

That’s right, in the best case, the server just sends you over to the HTTPS version of the page anyway. It’s as if the teller at your bank carried cash deposits out the front door, walking them around the building before reentering the bank and carrying them to the vault!

Okay, so, what’s a security-conscious person to do?

First, recognize the problem. If you stumble across a “HTTP” reference, it’s a security bug. Either fix it, or complain to someone who can.

Next, actively seek-and-destroy non-secure references.

A New Category of Mixed Content?

Web developers are familiar with two categories of Mixed Content: Active Mixed-Content (e.g. script) which is blocked by default, and Passive Mixed-Content (images, etc), which browsers tend to allow by default, usually with the penalty of removing the lock from the address bar.

However, secure pages with non-secure links don’t trigger ANY warning in the browser.

For now, let’s call the problem described in this post Latent Mixed Content.

Finding Latent Mixed Content

Finding HTTP links isn’t hard, but it can be tedious. To that end, between late-night feedings of my newborn, I’ve been learning Chrome’s extension model– a wonderful breath of fresh air after years of hacking together COM extensions in IE. The result of that effort is now available for your bug-hunting needs.

Download the moarTLS Chrome Extension.

#icanhazthecodez? Sure.

The extension adds an unobtrusive button to Chrome’s toolbar. The extension is designed to have little-to-no impact on the performance or operation of Chrome unless you actively interact invoke the extension.

When the Button button is clicked, the extension analyzes the current page to find out which hyperlinks (<a> elements) are targeting a non-secure protocol. If the page is free of non-secure links, the report is green:

PayPal showing all green

If the current page’s host sends a HTTP Strict Transport Security directive, a green lock is shown next to the hostname at the top of the report: green lock. Click the hostname to launch the SSLLabs Server Test for the host to explore what secure protocols are supported and find any errors in the host’s certificate or TLS configuration.

If the page contains one or more non-secure links, the report gets a yellow background and the non-secure links are listed:

Yellow warning report, 4 non-secure links

The non-secure links in the content of the page are marked in red for ease-of-identification:

Four Red links in the page

Alt+Click (or Ctrl+Click) on any entry in the report to cause the extension to probe the target hostname to see whether a HTTPS connection to the listed hostname is possible. If a HTTPS connection attempt succeeds, a grey arrow is shown. If the connection attempt fails (indicating that the server is only accessible via HTTP), a red X is shown:

Three grey up-arrows, one red X

If the target is accessible over HTTPS and the response includes a HTTP Strict Transport Security header, the grey arrow is replaced with a green arrow:

Green Arrow

Note: Accepting HTTPS connections alone doesn’t necessarily indicate that the host completely supports HTTPS—the secure connection could result in error pages or redirections to a redirection back to HTTP. But a grey arrow indicates that at least the server has a valid certificate and is listening  for TLS connections on port 443. Before updating each link to HTTPS, verify that the expected page is returned.

Returning to our original example, Fidelity’s non-secure links are readily flagged:

Non-secure links

If you read your email in a web client like GMail or Hotmail, you can also check whether your HTML emails are providing secure links:

Insecure credit card


HTTP-Delivered Pages

The examples above presuppose that the current page was delivered over HTTPS. If the page itself was delivered non-securely (over HTTP), invoking the moarTLS extension colors the background of the page itself red. In the report flyout, the hostname shown at the top is prefixed with http/. The icon adjacent to the domain name will either be an up-arrow:

…indicating that the host accepts HTTPS connections, or a red-X, indicating that it does not:

The extension exposes the option (simply right-click the icon) to flip insecurely-delivered images:

moarTLS options

When this option is enabled, images delivered insecurely are flipped vertically, graphically demonstrating one of the least malicious actions a Man-in-the-Middle could undertake when exploiting a site’s failure to use HTTPS.

Upside-down images

The Warn on non-secure downloads option instructs the extension to warn you when a file download occurs if either the page linking to a download, or the download itself, used a non-secure protocol:

Non-secure download

Non-secure file downloads are extremely dangerous; we’ve already seen attacks in-the-wild where a MITM intercepts such requests and responds with malware-wrapped replacements. Authenticode-signing helps mitigate the threat, but it’s not available everywhere, and it should be bolstered with HTTPS.


This extension has a number of limitations; some will be fixed in future updates.

False Negatives

  • moarTLS looks only at the links in the markup. JavaScript could intercept a link click and cause an non-secure navigation when the user clicks a link with an otherwise secure HREF.
  • moarTLS does not currently check the source of CSS background images.
  • moarTLS does not currently mangle insecurely-delivered fonts, audio, or video.
  • moarTLS only evaluates links currently in the page. If links are added later (e.g. via AJAX calls), they’re not marked unless you click the button again.

False Positives

  • moarTLS looks only at the links in the markup. JavaScript could intercept a link click and cause an secure navigation when the user clicks a link with an otherwise non-secure HREF. Arguably this isn’t a false-positive because the user may have JavaScript disabled.
  • moarTLS looks only at the link, and does not exempt links which are automatically upgraded by the browser due to a HSTS rule. Arguably this isn’t a false-positive because not all browsers support HSTS, and the user may copy a URL to a non-browser client (e.g. curl, wget, etc).
  • moarTLS isn’t aware of upgrade-insecure-requests, although that only helps for same-origin navigations. Arguably this isn’t a false-positive because not all browsers support this CSP directive, and the user may copy a URL to a non-browser client (e.g. curl, wget, etc).
  • moarTLS isn’t aware of block-all-mixed-content. Arguably this isn’t a false-positive because not all browsers support this CSP directive, and the user may copy a URL to a non-browser client (e.g. curl, wget, etc).


Q1. Why is this an extension? Shouldn’t it be in the Developer Tools’ Security pane, which currently flags active and passive mixed content:

Security Report

A1. Great idea. :)

Q2. How do I examine “popups” which don’t show the Chrome toolbar?

No toolbar

A2. Use “Show as Tab” on the system menu:

System Menu command Show As Tab


Q3. How much of the Web is HTTPS today?

A3. See

Published by ericlaw

Impatient optimist. Dad. Author/speaker. Created Fiddler & SlickRun. PM @ Microsoft 2001-2012, and 2018-2022, working on Office, IE, and Edge. Now a SWE on Microsoft Defender Web Protection. My words are my own, I do not speak for any other entity.

9 thoughts on “Seek and Destroy Non-Secure References Using the moarTLS Analyzer

    1. I don’t know of a better place to report these to Google at the moment, but we’re starting to chase down these problems in common code and that should fix a huge number of pages.

    1. I hope to make this available for Firefox and Edge eventually, as both are adopting Chrome’s model for extensions.

      1. I now have this extension mostly working in Firefox’s Nightly build. When it’s stable, I’ll submit it to Mozilla.

  1. Good one. Flip image works works on majority of the images but saw a case where ads served by a 3rd party did not get flipped. Not easy to reproduce though

    1. Repro URLs would be great! The most likely explanations are either

      1. The ad image was delivered securely
      2. the ad is using the image as a background-image in CSS, or
      3. the ad is rendered using either a Flash applet or a Canvas element.
  2. Thanks, I can reproduce this. The 2nd ad I see on this page “looks” like an animated image, but it’s actually an IFRAME in which there are containing text and images. The images are rendered as CSS background-images and thus hit the limitation.

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