Feeds

CERT: Linux servers under 'Phalanx' attack

Stolen keys unlock back door

Securing Web Applications Made Simple and Scalable

Attacks in the wild are under way against Linux systems with compromised SSH keys, the US Computer Emergency Readiness Team is warning.

The attacks appear to use stolen SSH keys to take hold of a targeted machine and then gain root access by exploiting weaknesses in the kernel. The attacks then install a rootkit known as Phalanx2, which scours the newly infected system for additional SSH keys. There's a viral aspect to this attack. As new SSH keys are stolen, new machines are potentially vulnerable to attack.

The CERT advisory makes no mention of the flaw in the Debian random number generator, but that's most likely the starting point for the attack. The flaw caused SSL keys generated for more than a year to be so predictable that they could be guessed in a matter of hours. Debian fixed the flaw in May.

Once a Linux server using a weak key is identified and rooted, it quickly gives up the keys it uses to connect to other servers. Even if these new keys aren't vulnerable to the Debian debacle, attackers can potentially use them to access the servers that use them if both the private and public parts of the key are included. Additionally, attackers can identify other servers that have connected to the infected machine recently, information that may enable additional breaches.

Phalanx2 is a derivative of a rootkit known as Phalanx. According to Packet Storm, Phalanx is a self-injecting kernel rootkit designed for the Linux 2.6 branch that hides files, processes and sockets and includes tools for sniffing a tty program and connecting to it with a backdoor. Phalanx2 is been updated to systematically steal SSH keys.

Fortunately, Phalanx2 is relatively easy to detect. One tell-tale sign: typing "ls" at a command prompt fails to show a directory "/etc/khubd.p2/" even though it can be accessed using the "cd" command. Additionally, the "/dev/shm/" directory may contain files used in the attack.

Several tools, including this one, can be used to sniff out vulnerable keys. CERT is also advising keys use strong passphrases or passwords to reduce the risk of a key is stolen.

"I'm still absolutely adamant this is a problem system administrators should have handled a long time ago," said Bill Stearns, a security researcher and incident handler for the SANS Internet Storm Center. "It's a really big issue. If they haven't figured it out, someone will do it for them." ®

The smart choice: opportunity from uncertainty

More from The Register

next story
Mozilla fixes CRITICAL security holes in Firefox, urges v31 upgrade
Misc memory hazards 'could be exploited' - and guess what, one's a Javascript vuln
Manic malware Mayhem spreads through Linux, FreeBSD web servers
And how Google could cripple infection rate in a second
How long is too long to wait for a security fix?
Synology finally patches OpenSSL bugs in Trevor's NAS
Don't look, Snowden: Security biz chases Tails with zero-day flaws alert
Exodus vows not to sell secrets of whistleblower's favorite OS
Roll out the welcome mat to hackers and crackers
Security chap pens guide to bug bounty programs that won't fail like Yahoo!'s
HIDDEN packet sniffer spy tech in MILLIONS of iPhones, iPads – expert
Don't panic though – Apple's backdoor is not wide open to all, guru tells us
Researcher sat on critical IE bugs for THREE YEARS
VUPEN waited for Pwn2Own cash while IE's sandbox leaked
prev story

Whitepapers

Top three mobile application threats
Prevent sensitive data leakage over insecure channels or stolen mobile devices.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Designing a Defense for Mobile Applications
Learn about the various considerations for defending mobile applications - from the application architecture itself to the myriad testing technologies.
Build a business case: developing custom apps
Learn how to maximize the value of custom applications by accelerating and simplifying their development.