Beware Of New Backdoor Malware Targeting Linux Users

The name Kevin Beaumont may not be familiar to you, but if you’re a Linux or Solaris user, he may have just saved you a whole lot of grief.

Recently, Mr. Beaumont discovered a stealthy backdoor malware that has been quietly infecting Linux and Solaris SPARC systems for more than five years.  BPFdoor only parses ICMP, UDP and TCP packets checking them for a specific data value and in the case of UDP and TCP packets, also checking for a password.

It can sit quietly on an infected system for an extended period. However,  once triggered, it allows the hacker who placed it there complete access to a compromised device.  Beaumont found BPDdoor activity on networks all over the world.  It was most notably found in South Korea, Hong Kong, India, Vietnam, Myanmar, Turkey and of course, the United States.

He also discovered eleven different speed test servers infected with BPFdoor. Although he was at a loss to explain how those systems may have been compromised since they run on closed-source software.

A different researcher named Craig Rowland issued a comprehensive technical report on BPFdoor and outlined some of its very clever anti-evasion tactics.

The tactics include the fact that it:

• Resides in system memory and deploys anti-forensics action (wipes the process environment, albeit unsuccessfully as it leaves it empty)
• Loads a Berkeley Packet Filter (BPF) sniffer allowing it to work in front of any locally running firewalls to see packets
• Modifies ‘iptables’ rules when receiving a relevant packet to allow attacker communication through the local firewall
• Masquerades the binary under a name like a common Linux system daemon
• Renames and runs itself as /dev/shm/kdmtmpflush
• Changes the date of the binary (time stamping) to October 30, 2008, before deleting it

Thanks to the research of these two individuals, an incredibly stealthy malware strain that specifically targets Linux and Solaris systems has now been exposed to sunlight.  Although the malware is well-designed and contains several clever anti-evasion tactics, now that the word is out, IT Security professionals know what to look for and can begin the process of purging it from infected systems.  Kudos to both.