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computer vulnerability bulletin CVE-2010-3856

glibc: privilege elevation via LD_AUDIT and constructor

Synthesis of the vulnerability

A local attacker can use the LD_AUDIT variable and the constructor of a system library, in order to obtain privileges of suid/sgid programs.
Vulnerable products: Debian, Fedora, Mandriva Linux, openSUSE, RHEL, Slackware, SLES, ESX.
Severity of this weakness: 2/4.
Consequences of an attack: administrator access/rights, privileged access/rights.
Hacker's origin: user shell.
Creation date: 25/10/2010.
Revision date: 07/11/2014.
Références of this bulletin: BID-44347, CERTA-2002-AVI-272, CVE-2010-3856, DSA-2122-1, DSA-2122-2, FEDORA-2010-16641, FEDORA-2010-16655, FEDORA-2010-16851, MDVSA-2010:212, openSUSE-SU-2010:0912-1, openSUSE-SU-2010:0913-1, openSUSE-SU-2010:0914-1, RHSA-2010:0793-01, RHSA-2010:0872-02, SSA:2010-301-01, SUSE-SA:2010:052, VIGILANCE-VUL-10068, VMSA-0001.3, VMSA-2011-0001, VMSA-2011-0001.1, VMSA-2011-0001.2, VMSA-2011-0001.3.

Description of the vulnerability

The glibc/ld.so program dynamically loads libraries.

The LD_AUDIT environment variable indicates an object list (Link-Auditing interface), that ld.so has to load.

When a program is suid or sgid, libraries indicated in LD_AUDIT are only loaded if they are located in a system library (such as /lib).

However, constructors of some libraries in /lib were not securely conceived. For example, the constructor of /lib/libpcprofile.so (installed with the glibc package) accepts to create a file with a name indicated in the PCPROFILE_OUTPUT variable.

A local attacker can therefore use the LD_AUDIT variable and the constructor of libpcprofile.so, in order to obtain privileges of suid/sgid programs.
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