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Vigil@nce - Linux kernel: weakness of ASLR via randomize_stack_top
February 2015 by Vigil@nce
This bulletin was written by Vigil@nce : http://vigilance.fr/offer
SYNTHESIS OF THE VULNERABILITY
An attacker can use a weakness of ASLR of the Linux kernel, in
order to more easily guess a stack address.
Impacted products: Linux
Severity: 1/4
Creation date: 13/02/2015
DESCRIPTION OF THE VULNERABILITY
Systems use ASLR in order to randomize memory addresses used by
programs and libraries.
The randomize_stack_top() function of the fs/binfmt_elf.c file
randomizes stack addresses. However, it uses a 32 bit integer to
store 34 bits, so two bits of random are lost. An attacker thus
have four more chances to bypass ASLR (268 million values, instead
of 1 billion).
An attacker can therefore use a weakness of ASLR of the Linux
kernel, in order to more easily guess a stack address.
ACCESS TO THE COMPLETE VIGIL@NCE BULLETIN
http://vigilance.fr/vulnerability/Linux-kernel-weakness-of-ASLR-via-randomize-stack-top-16193
