Shellshock used to spread Mayhem

Posted by   Virus Bulletin on   Oct 8, 2014

Malware switched to more effective Perl installer.

One of the most prominent discussion topics during VB2014 was the 'Shellshock' vulnerability (CVE-2014-6271) in the popular Bash shell for *nix, which was publicly disclosed while the conference was going on in Seattle.

  The name 'Shellshock' started as a joke on Twitter.

Considered at least as serious as Heartbleed, Shellshock affects millions of servers. A successful exploit allows an attacker to execute arbitrary code by making use of the fact that many processes set environment variables in Bash and, under certain circumstances, Bash execute commands concatenated to the end of such variables.

Although exploiting the vulnerability isn't as straightforward as it is for Heartbleed, the potential attack surface is much larger and a lucky attacker might even be able to exploit the vulnerability on a server that is not exposed to the Internet. I wouldn't be surprised if, for some time to come, we learn of attacks using Shellshock for lateral movement or to escalate privileges in an advanced attack.

Cybercriminals are already exploiting Shellshock through the most obvious attack vector: vulnerable web servers. On its blog, ZScaler has an overview of various such attacks seen in the wild.

One attack that I found particularly interesting was the use of Shellshock by the 'Mayhem' malware to spread further - something which Malware Must Die! wrote about yesterday.

Earlier this year, we published a paper on Mayhem by three researchers from Yandex in Russia. Mayhem is a piece of malware that runs on *nix servers and is noteworthy because it can act under restricted privileges. It uses various plug-ins to look for and infect other servers.

  Part of Mayhem's Perl installer. Source: Malware Must Die!

When Mayhem exploits Shellshock, it uses it to upload and run an installer written in Perl, thus replacing the original PHP-based installer.

I spoke to Evgeny Sidorov, one of the paper's authors, who said he wasn't surprised that Mayhem's owners are using Shellshock to infect more machines. The malware's flexible architecture made it easy for them to do so and using Shellshock is easier and more effective than brute-forcing WordPress credentials, which had hitherto been used. He also pointed out that using a Perl installer makes sense, given that Perl is installed on almost all *nix servers by default, while PHP is usually only an optional extra.

The good news if you're running Bash - and if you're running anything Linux- or Unix-based, you almost certainly are - is that patching is easy and that doing so is very unlikely to break other software. There is no excuse not to patch.

Posted on 08 October 2014 by Martijn Grooten

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

 

Latest posts:

VB2021 call for papers - now open, to all!

The call for papers for VB2021 is now open and we want to hear from you - we're planning for flexible presentation formats, so everyone is encouraged to submit, regardless of whether or not you know at this stage whether you'll be able to travel to…

In memoriam: Yonathan Klijnsma

We were very sorry to learn of the passing of researcher Yonathan Klijnsma last week. Here, former VB Editor Martijn Grooten shares his memories of a talented researcher and a very kind person: this month, infosec lost a really good one.

VB2020 localhost videos available on YouTube

VB has made all VB2020 localhost presentations available on the VB YouTube channel, so you can now watch - and share - any part of the conference freely and without registration.

VB2020 presentation & paper: 2030: backcasting the potential rise and fall of cyber threat intelligence

At VB2020 localhost, threat intelligence consultant Jamie Collier used the analytical technique of backcasting to look at the rise and fall of the cyber threat intelligence industry.

VB2020 presentation: Behind the Black Mirror: simulating attacks with mock C2 servers

At VB2020 localhost, Carbon Black's Scott Knight presented an approach he and his colleagues have taken to more realistically simulate malware attacks.

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.