1 in 500 secure connections use forged certificate

Posted by   Virus Bulletin on   May 13, 2014

For reasons ranging from relatively good, to actual malware.

Researchers from Facebook and Carnegie Mellon University have published a paper (PDF) in which they show that out of a sample of over 3 million secure connections to Facebook, 0.2% used a forged SSL certificate.

SSL and its successor TLS are encryption protocols that protect many Internet connections, including those using HTTPS, the secure version of HTTP. SSL/TLS does this by doing two things: first, it makes sure the connection is encrypted. Secondly, it allows the client to authenticate the identity of the server.

The second part matters: it means that a connection attempt to a secure server should fail if, for instance because of a malicious DNS configuration, a connection is made to a fake server set up by an attacker. It also prevents man-in-the-middle attacks, where a connection to the real server is 'broken' into two encrypted parts by a malicious actor placed somewhere in the middle.

Provided the certificate presented by the other end of the connection is actually forged (and not maliciously obtained from a legitimate certificate authority, as we saw in the case of DigiNotar), the client will automatically end the connection. Or, if a human is behind the client, they will be given a clear warning that they should only continue if they know what they're doing.

From the server's point of view, it is generally not possible to detect the fact that a client is connecting through a forged certificate. The researchers, however, found a way around this by using a Shockwave Flash applet that initiates an SSL/TLS connection, parses the certificate presented by the other end, and sends this result to the real server. They used this to detect any forged certificates being used when clients connected to Facebook.

While this didn't always work - for a number of reasons, out of more than 9 million connections made, a well-formed certificate could be read from only 3.4 million of them - it worked in enough cases for statistics to be performed. The researchers did point out that their detection method can fairly easily be evaded by an attacker who is aware of it.

Out of the 3.4 million certificates, a little under 7,000 (or about 0.2%) turned out not to be legitimate. The number may seem small, but it is not insignificant, especially given the sheer volume of HTTPS connections made over the Internet every day.

Not all of these fake certificates are actually malicious: in many cases they were issued by anti-virus software running on the device itself, or by a firewall product running on the gateway. The researchers make the (probably correct) assumption that these certificates were explicitly or implicitly installed by the users and do not consider this to be a problem in itself.

Still, they rightly point out that such certificates could introduce an extra weakness. It is, for instance, possible that the issuer of such a certificate could be compelled to hand over their signing keys to a government. And in the case of Cyberoam, all of the company's appliances used the same private signing key, which could be read by anyone owning such an appliance (an issue which has since been resolved).

In some cases, however, the researchers found the forged certificate to be included with a definite malicious purpose. They detected 112 certificates issued by 'IopFailZeroAccessCreate', something they could link to malware.

The paper makes an interesting read, both for the methodology used and the conclusions it reaches. SSL/TLS works well in almost all cases. But given the billions of supposedly secure connections made on a daily basis, 'almost all' isn't good enough.

Posted on 13 May 2014 by Martijn Grooten

twitter.png
fb.png
linkedin.png
hackernews.png
reddit.png

 

Latest posts:

VB2019 conference programme announced

VB is excited to reveal the details of an interesting and diverse programme for VB2019, the 29th Virus Bulletin International Conference, which takes place 2-4 October in London, UK.

VB2018 paper: Under the hood - the automotive challenge

Car hacking has become a hot subject in recent years, and at VB2018 in Montreal, Argus Cyber Security's Inbar Raz presented a paper that provides an introduction to the subject, looking at the complex problem, examples of car hacks, and the…

VB2018 paper and video: Android app deobfuscation using static-dynamic cooperation

Static analysis and dynamic analysis each have their shortcomings as methods for analysing potentially malicious files. Today, we publish a VB2018 paper by Check Point researchers Yoni Moses and Yaniv Mordekhay, in which they describe a method that…

VB2019 call for papers closes this weekend

The call for papers for VB2019 closes on 17 March, and while we've already received many great submissions, we still want more!

Registration open for VB2019 ─ book your ticket now!

Registration for VB2019, the 29th Virus Bulletin International Conference, is now open, with an early bird rate available until 1 July.

We have placed cookies on your device in order to improve the functionality of this site, as outlined in our cookies policy. However, you may delete and block all cookies from this site and your use of the site will be unaffected. By continuing to browse this site, you are agreeing to Virus Bulletin's use of data as outlined in our privacy policy.