Linux exploit evades security barrier

A security hole in the Linux kernel, which allows security features in the operating system to be bypassed, affects Red Hat Enterprise Linux 5, according to a security researcher
Written by Tom Espiner, Contributor
A security researcher has released zero-day code for a flaw in the Linux kernel, saying that it bypasses security protections in the operating system.

The source code for the exploit was made available last week by researcher Brad Spengler on the Dailydave mailing list. According to the researcher, the code exploits a vulnerability in Linux version 2.6.30, and 2.6.18, and affects both 32-bit and 64-bit versions. The 2.6.18 kernel is used in Red Hat Enterprise Linux 5.

The exploit bypasses null pointer de-reference protection in the mainline kernel, which could allow an attacker to gain root control of a system, Spengler wrote.

It also uses arbitrary code execution to disable security features such as auditing, Security-Enhanced Linux (SELinux), AppArmor and Linux Security Module, while making the applications running outside the kernel believe that SELinux is still operating.

In the notes for his source code, Spengler said the exploit is strengthened if SELinux is applied to the operating system. SELinux is a set of modifications that can be applied to the kernel to harden it, by providing a set of security policies.

"Having SELinux enabled actually weakens system security for these kinds of exploits," he wrote.

Security training organization the Sans Institute called the exploit "fascinating". In a blog post on Friday, Sans Institute incident handler Bojan Zdrnja said that the exploit uses the Linux compiler to overcome the security features.

"The compiler will introduce the vulnerability to the binary code, which didn't exist in the source code," wrote Zdrnja. "This will cause the kernel to try to read/write data from 0x00000000, which the attacker can map to userland — and this finally pwns the box."

In his notes on the source code, Spengler said that a workaround would be for administrators to compile the kernel with fno-delete-null-pointer-checks.

This article was originally posted on ZDNet UK.

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