Firefox joins Chrome in supporting HTTP Strict Transport Security (HSTS)

Filed Under: Data loss, Privacy

Firefox logoAlthough the Firefox team has an entire page on the website dedicated to the new security features in Firefox 4, they seem to have forgotten to mention HTTP Strict Transport Security (HSTS).

While HSTS may not be the sexiest security feature for the average Joe, I was thrilled to see it implemented in the world's second most popular browser. Google Chrome has supported HSTS since September, 2009 in versions and higher.

What is HSTS? Currently it is a draft RFC that tries to address some of the insecurities present in the HTTPS specification.

The easiest way to describe the core idea is that it allows a website operator to describe how they want the use of SSL to be handled for their domain. Supporting web browsers will honor HTTP headers and ensure this security policy is applied.

As an example, has elected to use HSTS headers on their service. The first time you visit from a compliant browser, your browser will receive a header that explains that PayPal should only be accessed via HTTPS and that any browser certificate errors should not allow the user to override them.

Sophos SSL cert

When specifying this header the website can also specify a Time To Live (TTL). This allows the updating of security certificates and changes in certificate authorities without a denial of service.

After receiving this header, if you try to surf to, your browser will automatically intercept the request and not send anything unencrypted across your network connection so long as you visit the site before the TTL expires. It will reformat your request to HTTPS and only communicate over SSL/TLS with PayPal.

The second important action is the ability for sites to not allow you to override certificate errors. We have mentioned previously the tendency for every day internet users to click yes/accept/ok to any prompt that is presented.

Online banking sites, financial sites or even Facebook and GMail now have the option to not only enforce HTTPS for users of compliant browsers, but also limit the ability for users to harm themselves through a lack of understanding of technical warnings.

I hope that Microsoft and Apple adopt this draft standard sooner rather than later to provide security for nearly all web surfers. While it has not yet been ratified, this proposal has my support and can make the web a safer place.

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7 Responses to Firefox joins Chrome in supporting HTTP Strict Transport Security (HSTS)

  1. Pete · 1658 days ago

    My org inspects HTTPS before we allow users to see the content. Obviously done using MIM techniques at the security boundary. I suspect we'd prefer a non compliant browser, or else we'd use compliant browsers to better secure internal transactions, but would want to modify the HTTP headers for Internet based sites to ensure SSL inspection could still take place. HSTS sounds like a bit of a dream for hackers to better get their malware into orgs. ps isn't Mutual TLS just as effective??

    • Chester Wisniewski · 1657 days ago

      If your solution (like our Sophos Web Appliance) is not actually performing a man-in-the-middle trying to masquarade as the original CA, but is a trusted authority for your clients then this still works fine. The self-signed certificate that is intercepting HTTPS and inspecting it simply must be trusted by the client.

  2. Mike Preston · 1658 days ago

    I still waiting for the new SSL stuff to finally be implemented. The standard that allows a normal HTTP connection to be renegotiated to SSL after some headers have been sent.

    This would allow SSL vhosts on a single IP to be used and it would remove the biggest hurdle to the whole world using SSL for normal browsing...

  3. Richard · 1658 days ago

    "The first time you visit ..."

    I thought HSTS headers could only be sent over an HTTPS connection? Otherwise, a MITM attack could specify HSTS for a host that doesn't support SSL, resulting in a DoS.

  4. "your browser will automatically intercept the request and not send anything unencrypted across your network connection"

    Tricky statement. When I looked at the HTTPS Everywhere extension from EFF for Firefox, and tried to find comparable extensions or plug-ins for other browsers, it seems that nearly all major browsers reject pre-fetching interception and rewriting of URLs. Thus, if you use Chrome or Safari, any HTTPS force option there will allow a user to visit the unencrypted site first (if that's the URL they provide), at which point any valid tokens in cookies are sent in the clear before a redirect happens to the secure site.

    I should go read the HSTS spec, but it seems like there would have to be a commitment from sites to not write tokens into cookies on non-secure versions of their sites if they want users to rely on SSL/TLS. Or the implementation of HSTS should perform a head request before sending cookies on the first visit within a period of time to determine whether the full request should be sent.

    Has this been considered here?

  5. Occulter · 1240 days ago

    A relatively new extension for Firefox called HTTPtoHTTPS can be used in addition HTTPS Everywhere. I just used it on this site and with Waterfox, and it locked the site (with no restart), affording AES-256 encryption. It can be found here:

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About the author

Chester Wisniewski is a Senior Security Advisor at Sophos Canada. He provides advice and insight into the latest threats for security and IT professionals with the goal of providing clear guidance on complex topics. You can follow Chester on Twitter as @chetwisniewski, on as Chester, Chester Wisniewski on Google Plus or send him an email at