Critical remote code execution flaw patched in Samba

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Security researchers are urging users to install new Samba security updates in order to address a critical vulnerability that allows attackers to execute arbitrary code with root privileges.

Samba is an implementation of the SMB/CIFS networking protocol that enables Unix-like systems, including Linux, BSD, Solaris and Mac OS X to share files and printers with Windows computers. It also allows such systems to be integrated into Microsoft Active Directory environments and even act as domain controllers.

The new vulnerability is located in the smbd file server and was discovered by Richard van Eeden of Microsoft Vulnerability Research.

“It can be exploited by a malicious Samba client, by sending specially-crafted packets to the Samba server,” the Red Hat security team said in a blog post. “No authentication is required to exploit this flaw. It can result in remotely controlled execution of arbitrary code as root.”

All versions of Samba from 3.5.0 to 4.2.0rc4 are vulnerable. The Samba project released versions 4.2.0rc5, 4.1.17, 4.0.25 and 3.6.25 to address the issue and also made code patches available.

Updated Samba packages were released by multiple Linux distributions including Red Hat Enterprise Linux, Ubuntu, Debian, Fedora and Suse. Users are advised to install the updates as soon as possible.

For Samba 4.0.0 and above there is a manual workaround that involves adding the line rpc_server:netlogon=disabled to the [global] section in the smb.conf file.

The Samba service is not normally configured to be accessible from the Internet, so any potential attackers looking to exploit this flaw would generally need to be inside the same network as an affected server, said Carsten Eiram, the chief research officer of vulnerability intelligence firm Risk Based Security, via email.

“It’s certainly not every day we see such vulnerabilities in high profile and widely used products like Samba,” Eraim said, adding that the flaw is quite severe. “Samba has released updated versions for 4 different branches as well as patches. I highly recommend anyone using Samba to apply those immediately.”

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