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Vulnerability of OpenBSD: denial of service via AltiVec

Synthesis of the vulnerability 

A local attacker can generate an Assist AltiVec exception in order to stop kernel.
Impacted products: OpenBSD.
Severity of this bulletin: 1/4.
Creation date: 30/04/2007.
Références of this threat: VIGILANCE-VUL-6771.

Description of the vulnerability 

PowerPC processors support AltiVec/VMX instructions, which are used for floating-point operations. Some of these instructions can generate an "assist" exception to indicate that received input are not normalized.

However, OpenBSD kernel does not handle this kind of exception, which leads to a stop.

A local attacker may therefore force processor to generate an "assist" exception, in order to create a denial of service.
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This cybersecurity announce impacts software or systems such as OpenBSD.

Our Vigil@nce team determined that the severity of this threat alert is low.

The trust level is of type unique source, with an origin of user shell.

An attacker with a expert ability can exploit this computer weakness alert.

Solutions for this threat 

OpenBSD 3.9: patch for AltiVec.
A patch is available:
  ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.9/macppc/023_altivec.patch

OpenBSD 4.0: patch for AltiVec.
A patch is available:
  ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.0/macppc/013_altivec.patch

OpenBSD: several patches.
After availability of version 4.1, several patches were published:
  ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.1/macppc/006_altivec.patch
  ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.1/common/005_route6.patch
  ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.1/common/004_xorg.patch
  ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.1/common/002_splnet.patch
  ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.1/common/001_mbuf.patch
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