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Vulnerability of Linux kernel: denial of service of VFAT

Synthesis of the vulnerability 

On a 64 bits processor, a local attacker can create a denial of service by using a VFAT ioctl.
Vulnerable software: Debian, Linux, RHEL.
Severity of this announce: 1/4.
Creation date: 02/11/2007.
Références of this computer vulnerability: BID-24134, CERTA-2002-AVI-197, CVE-2007-2878, DSA-1479-1, RHSA-2007:0939-01, VIGILANCE-VUL-7303.

Description of the vulnerability 

The kernel_dirent structure stores information about a directory.

The VFAT_IOCTL_READDIR_BOTH ioctl is used to read directories on a VFAT filesystem.

However, on a 64 bits architecture, using this ioctl corrupts the kernel_dirent structure. Kernel then stops when it is first used.

A local attacker can therefore create a denial of service.
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This security vulnerability impacts software or systems such as Debian, Linux, RHEL.

Our Vigil@nce team determined that the severity of this computer weakness bulletin is low.

The trust level is of type confirmed by the editor, with an origin of user shell.

A proof of concept or an attack tool is available, so your teams have to process this alert. An attacker with a technician ability can exploit this security note.

Solutions for this threat 

Linux kernel: version 2.6.21.2.
Version 2.6.21.2 is corrected:
  http://www.kernel.org/

Debian 4.0: new linux-2.6 packages.
New packages are available.
The installation procedure is indicated in the announce.

RHEL 4: new kernel packages.
New packages are available:
Red Hat Enterprise Linux version 4: kernel-2.6.9-55.0.12
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