Samba patch issued for buffer overflow vulnerability

A software buffer overflow vulnerability in Samba open-source software could give an attacker remote access to a machine running that software, according to security company Digital Defense Inc.

The Samba Team, a group that manages the open-source software, released patches Monday and a new version of the software, Samba 2.2.8a, to address the vulnerability. Samba is a widely used software package that enables users to access and use files, printers and other shared resources on a corporate intranet or on the Internet.

Samba works with a variety of operating systems, including Linux, Unix, OpenVMS and OS/2 and allows files hosted on machines running those operating systems to share files with machines running versions of the Microsoft Corp. Windows operating system.

The buffer overflow vulnerability disclosed Monday by Digital Defense is due to an improperly written function within the Samba code.

Buffer overflows occur when a process tries to store more data in a buffer, or temporary data storage area, than it was intended to hold. Malicious hackers can use buffer overflows to place and execute code on compromised machines.

The new vulnerability has been known about within hacking circles for more than a month and was already being used to attack vulnerable systems on the Internet before the Digital Defense advisory was released, according to a security expert with knowledge of the hacking community.

In its advisory, Digital Defense, in San Antonio, Texas, said that it detected an active exploit using the Samba vulnerability on a test system it set up on the Internet.

However, Digital Defense may be to blame for some of those exploits.

Along with its advisory, Digital Defense Monday accidentally posted its own exploit code, a script named "trans2root.pl" on its Security Tools page. (See http://www.digitaldefense.net/labs/securitytools.html.)

When run against a vulnerable system, the exploit provided by Digital Defense would give an attacker total access to the remote system.

"It was an unfortunate incident. We had an individual who was overzealous and released a script we had developed for internal development and testing of the vulnerability," said Rick Fleming, chief technology officer at Digital Defense.

The script was available for download from Digital Defense for approximately 12 hours, but no figures were available on how many copies of the file were downloaded during that time, Fleming said.

While it is common for Digital Defense to release tools that detect and test for the vulnerabilities the company uncovers, the trans2root.pl file was not an example of such a tool, according to Fleming.

"Tools are usually a proof of concept. They're not things that anyone can run. You need a programming background to effectively use the tool," he said.

In addition, Digital Defense usually waits at least a month after the release of a patch from the vendor to release a tool, depending on the severity of the vulnerability. In some cases, no tool is released, Fleming said.

Responding to the mishap, Digital Defense changed its policies that cover the release of advisories. Sign off from senior management in the form of a digital signature is now required before the release of any information, Fleming said.

Samba is a standard part of many Linux and Unix distributions including those released by Red Hat Inc., MandrakeSoft SA and Debian. All previous versions of Samba up to version 2.2.8 are affected by the vulnerability.

Despite the fact that the vulnerability is widespread, it is unlikely that it could be exploited from remote users on the Internet, according to Fleming.

"We found very few instances, if any, of somebody who has a Samba share on their extranet side. If they did (have such a share) it was on a server that already gives access to everybody anyway," Fleming said.

The risk for most Samba users is from internal attacks, he said.

Digital Defense urged Samba users to check their Samba servers for signs of compromise and to apply patches for the vulnerability or upgrade to Samba 2.2.8a. (See http://www.samba.org.)

By Monday, major Linux and Unix vendors were notifying users of the problem and releasing software updates that fixed the Samba vulnerability for their own products.

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Paul Roberts

IDG News Service
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