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 vice president and head of Trustwave SpiderLabs, says the flaw affects anyone who has embedded Linux-based appliances that use Samba for file sharing, such as NASes, 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.

[While operating systems and PC applications have evolved fast patch mechanisms, the proliferation of slow-to-patch embedded devices leaves companies vulnerable. See Firms Slow To Secure Flaws In Embedded Devices.]

"Samba is not commonly exposed to the Internet, fortunately. However, most NAS devices, home storage systems, Linux PCs, and Mac OS X PCs that share files over SMB are based on Samba," says HD Moore, chief security officer for Rapid 7 and creator of Metasploit. "For example, I have a couple of home storage arrays that the vendor considers plug and play. In both cases, the SMB server is Samba-based, and not likely to see a patch anytime soon."

Moore says corporate, internal systems would be at risk of attack by malicious internal employees and intruders with access to the corporate network. But users don't always know that their embedded devices use Samba since most of these devices don't exactly broadcast that element, according to Moore.

"The real risk is long-term exploitability of NAS devices, smart printers, and other systems that use the Samba code and don't maintain security patches for the SMB service or systems that you never, ever want to take offline," Moore says.

That would include things such as a NAS: "Taking your NAS offline to patch a core service is something that typically involves a maintenance window and a lot of pain, depending on how many systems are using it," he says.

Meanwhile, Trustwave SpiderLabs posted a blog today on the Samba security update.

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