FreeBSD bug grants local root access

Trivial exploitation

A security researcher has uncovered a security bug in the FreeBSD operating system that allows users with limited privileges to take full control of underlying systems.

The bug in FreeBSD's kqueue notification interface makes it trivial for those with local access to a vulnerable system to gain full root privileges, Przemyslaw Frasunek, an independent security consultant in Poland, told The Register. It affects versions 6.0 through 6.4 of the operating system, the last two versions of which enjoy wide use and continue to be supported by the FreeBSD Foundation.

Versions 7.1 and and beyond are not vulnerable.

Those exploiting the bug must first have local access to a vulnerable system, either as a legitimate user or by exploiting some other flaw (say, a vulnerable PHP script) that gives an attacker a toe-hold in to the targeted system. Frasunek said the vulnerability is trivial to exploit, as a video he posted here suggests.

The bug is the result of a race condition in the FreeBSD kqueue that leads to a NULL pointer dereference in kernel mode. Attackers can cause vulnerable systems to run malware by putting the code in a memory page mapped to address 0x0.

Frasunek said he notified FreeBSD officials on August 29 and has yet to get a response. Robert Watson, a FreeBSD Core Team member, told El Reg that it appeared the email had gotten "lost in the slew" and he expected an advisory to be issued soon. ®

Updated to clarify on versions 6.3 and 6.4 continue to be supported and to add comment from a FreeBSD official.