NewsFebruary 27, 2017 @ 3:25 PM

Linux Update Fixes 11-Year-Old Flaw

Andrey Konovalov, a security researcher at Google, found a use-after-free hole within Linux, CSO Online reported. This particular flaw is of interest because it appears to be situational. It only showed up in kernels built with a certain configuration option — CONFIG_IP_DCCP — enabled.

Unfortunately, many popular Linux distributions have enabled this option by default. A new Linux update has since patched the vulnerability, although the exploit has been present in Linux kernels since 2005.

Don’t Fall in a Heap

The flaw allows cybercriminals to use heap spraying methods to execute arbitrary code inside the kernel and escalate permissions.

“If the overwritten object has any triggerable function pointers,” Konovalov wrote in his announcement, “an attacker gets to execute arbitrary code within the kernel.”

An attacker might hijack a low-permissions account, then use this hole to escalate the permissions that are given to that user. Even though this is a local escalation bug, it may be combined with other types of attacks that are amenable to remote exploitation. Then the local user is, in reality, a remote one.

This flaw dates back to 2005, when the Linux kernel started to support the Datagram Congestion Control Protocol (DCCP).

Linux Update Offers Quick Fix

Red Hat disclosed that Red Hat Enterprise Linux 5, 6, 7 and MRG 2 kernels were affected. Patches are currently available for Red Hat Enterprise Linux 6 and 7 and for the Red Hat Enterprise Linux for Real Time for NFV (v. 7) (kernel-rt).

While Debian 7 Wheezy and Debian 8 Jessie have also been fixed, Debian Stretch and Sid have yet to be patched. Additionally, patches are available for Ubuntu 12.04 LTS, 14.04 LTS, 16.04 LTS and 16.10.

Only Linux Enterprise Server 10 is affected in the SUSE distros. SUSE Linux Enterprise Server 11 SP 1 to 4 and SUSE Linux Enterprise Server 12 SP 1 and 2 do not support the problematic DCCP protocol.

Recent versions of the SELinux policy can also mitigate this problem, no matter what the enable state is set to. The policy can be configured to not load the DCCP module even if it is called. No module means no problems.

While this problem needs to be patched, administrators must ensure that they use the correct Linux update.

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Larry Loeb

Principal, PBC Enterprises

Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek. He wrote for IBM's DeveloperWorks site for seven years and has written a book on the Secure Electronic Transaction Internet protocol. His latest book has the commercially obligatory title of Hack Proofing XML. He's been online since uucp "bang" addressing (where the world existed relative to !decvax), serving as editor of the Macintosh Exchange on BIX and the VARBusiness Exchange.