A dangerous vulnerability in a pervasive tool for running Linux systems in a Windows environment leaves the door open for an attacker to access these systems without requiring any authentication.

The open-source Samba group this week released an update to the Samba program to fix a bug that could allow an attacker to remotely acquire root access to the targeted server. The bug in Samba versions 3.6.3 and previous versions is a buffer overflow flaw in Samba's remote procedure call code. "As this does not require an authenticated connection, it is the most serious vulnerability possible in a program, and users and vendors are encouraged to patch their Samba installations immediately," according to a newly issued advisory from Samba on the new CVE-2012-1182 vulnerability, which includes links to patches for the software.

Nicholas Percoco, senior VP and head of Trustwave SpiderLabs, says the flaw affects anyone who has embedded Linux-based appliances that use Samba for file sharing, such as network-attached storage (NAS), print servers, and printers. While these devices tend to run in an intranet rather than over the big Internet, the main risk would be from a sophisticated targeted attack or a malicious insider, he says.

"This is a very critical patch you should be applying ... if an attacker gets root access, it's game over from a security perspective," Percoco says. "You should not be running Samba [systems] on the Internet. That being said, it doesn't mean people aren't."

A proof-of-concept is circulating, and Percoco says the vulnerability is prime for abuse as a network worm, as well as for a targeted attack. "It can also be the perfect storm for a Unix-based worm. This is something like the Nimda For Linux/Unix," he says.

But most at risk here is the compromise of Linux-embedded systems that use Samba, and many of these device vendors are notorious for not regularly patching these systems. "Some have firmware that you can have updated. So contact the vendor to see if they have updated firmware for this," Percoco says. "If not, you have to weigh the risk. If you're risk-averse, you may have to unplug or replace these devices."

Many devices won't ever be fixed, Percoco and other security experts say.

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