Linux botnet Mayhem spreads through Shellshock exploits

The botnet targets Web servers that haven't been patched for recent vulnerabilities found in the Bash Linux shell

Shellshock continues to reverberate: Attackers are exploiting recently discovered vulnerabilities in the Bash command-line interpreter in order to infect Linux servers with a sophisticated malware program known as Mayhem.

Mayhem was discovered earlier this year and was thoroughly analyzed by researchers from Russian Internet firm Yandex. It gets installed through a PHP script that attackers upload on servers via compromised FTP passwords, website vulnerabilities or brute-forced site administration credentials.

Mayhem's main component is a malicious ELF (Executable and Linkable Format) library file that, after installation, downloads additional plug-ins and stores them in a hidden and encrypted file system. The plug-ins enable attackers to use the newly infected servers to attack and compromise additional sites.

In July, the Yandex researchers estimated that the botnet consisted of around 1,400 infected servers that connected to two separate command-and-control servers.

Researchers from independent research outfit Malware Must Die (MMD) reported earlier this week that Mayhem's authors have added Shellshock exploits to the botnet's arsenal.

Shellshock is the collective name for several vulnerabilities discovered recently in the Linux Bash command-line interpreter. They can be exploited to achieve remote code execution on servers through several attack vectors including the CGI (Common Gateway Interface), OpenSSH, DHCP (Dynamic Host Configuration Protocol) and even OpenVPN in some cases.

The Shellshock attacks originating from the Mayhem botnet target Web servers with CGI support. The bots probe Web servers to determine if they're vulnerable to the Bash flaws and then exploit them to execute a Perl script, according to the MMD researchers.

The script has the malicious Mayhem ELF binary files for both 32-bit and 64-bit CPU architectures embedded into it as hexadecimal data and uses the LD_PRELOAD function to extract and run them on the system, the researchers said in a blog post.

Like the previous version, it creates a hidden file system where it stores its additional components -- plug-ins -- that are used for various types of scanning and attacks against other servers. The MDL researchers suspect that one of those components has been updated to use the new Shellshock exploits, but haven't confirmed it yet.

However, this theory is supported by the fact that some of the observed Shellshock attack attempts have originated from IP (Internet Protocol) addresses associated with existing Mayhem bots in addition to new IP addresses from a variety of countries including the U.K., Indonesia, Poland, Austria, Australia and Sweden. MMD has shared the information it has gathered with national computer emergency response teams (CERTs).

Most Linux distributions have issued patches for the Shellshock vulnerabilities already, but many Web servers, especially self-managed ones, are not configured to deploy updates automatically. There are also many Linux-based enterprise products and embedded devices that include Web servers and are vulnerable to Shellshock. These can also be a target if patches for them haven't been deployed or are not yet available.

Join the Good Gear Guide newsletter!

Error: Please check your email address.

Tags patchessecurityMalware Must DieExploits / vulnerabilitiesmalwareYandex

Our Back to Business guide highlights the best products for you to boost your productivity at home, on the road, at the office, or in the classroom.

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lucian Constantin

IDG News Service
Show Comments

Most Popular Reviews

Latest News Articles

Resources

PCW Evaluation Team

Azadeh Williams

HP OfficeJet Pro 8730

A smarter way to print for busy small business owners, combining speedy printing with scanning and copying, making it easier to produce high quality documents and images at a touch of a button.

Andrew Grant

HP OfficeJet Pro 8730

I've had a multifunction printer in the office going on 10 years now. It was a neat bit of kit back in the day -- print, copy, scan, fax -- when printing over WiFi felt a bit like magic. It’s seen better days though and an upgrade’s well overdue. This HP OfficeJet Pro 8730 looks like it ticks all the same boxes: print, copy, scan, and fax. (Really? Does anyone fax anything any more? I guess it's good to know the facility’s there, just in case.) Printing over WiFi is more-or- less standard these days.

Ed Dawson

HP OfficeJet Pro 8730

As a freelance writer who is always on the go, I like my technology to be both efficient and effective so I can do my job well. The HP OfficeJet Pro 8730 Inkjet Printer ticks all the boxes in terms of form factor, performance and user interface.

Michael Hargreaves

Windows 10 for Business / Dell XPS 13

I’d happily recommend this touchscreen laptop and Windows 10 as a great way to get serious work done at a desk or on the road.

Aysha Strobbe

Windows 10 / HP Spectre x360

Ultimately, I think the Windows 10 environment is excellent for me as it caters for so many different uses. The inclusion of the Xbox app is also great for when you need some downtime too!

Mark Escubio

Windows 10 / Lenovo Yoga 910

For me, the Xbox Play Anywhere is a great new feature as it allows you to play your current Xbox games with higher resolutions and better graphics without forking out extra cash for another copy. Although available titles are still scarce, but I’m sure it will grow in time.

Featured Content

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?