Gravity: 2/4
 Consequences: administrator access/rights
 Provenance: user shell
 Means of attack: no proof of concept, no attack
 Ability of attacker: expert (4/4)
 Confidence: confirmed by the editor (5/5)
 Diffusion of the vulnerable configuration: high (3/3)
 Creation date: 04/09/2008
 Identifier: VIGILANCE-VUL-8087

IMPACTED PRODUCTS

 FreeBSD [confidential versions]

DESCRIPTION

The FreeBSD/amd64 system uses the GS segment to store:
 in user mode : information on threads
 in kernel mode : information on processes

The SwapGS assembler instruction swaps GS and the "KernelGSbase" MSR (Model Specific Register). This instruction is called for each mode change.

However, if a GPF (General Protection Fault) occurs when returning from an interrupt, trap or system call, SwapGS is called twice. Kernel GS data can thus be altered by the user.

A local attacker can therefore execute code with kernel privileges.

CHARACTERISTICS

 Identifiers: BID-31003, CVE-2008-3890, FreeBSD-SA-08:07.amd64, VIGILANCE-VUL-8087
 Url: https://vigilance.aql.fr/tree/1/8087