bugtraq - Linux ASLR mmap weakness: Reducing entropy by half

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Date: Tue, 21 Apr 2015 18:26:12 +0200
From: Hector Marco-Gisbert <hecmargi@....es>
To: fulldisclosure@...lists.org, fulldisclosure@...lists.org,
  bugtraq@...urityfocus.com
CC: Ismael Ripoll <iripoll@...ca.upv.es>,
  Assign a CVE Identifier <cve-assign@...re.org>
Subject: Linux ASLR mmap weakness: Reducing entropy by half

A bug in Linux ASLR implementation has been found. The issue is that the mmap 
base address for processes is not properly randomized on some architectures due 
to an improper bit-mask manipulation. Affected systems have reduced the mmap 
area entropy of the processes by half.

The number of possible locations are reduced by 50%, which for example will 
reduce the cost of brute force attacks.

PowerPC, Sparc64 and ARM have 18 bits of entropy. Non-vulnerable systems have 
262144 (2^18) different places to locate the mmap area. On vulnerable systems, 
this value is reduced to 131072 (2^17).

Advisory details at:
http://hmarco.org/bugs/linux-ASLR-reducing-mmap-by-half.html

-- 
Hector Marco-Gisbert @ http://hmarco.org/
Cyber Security Researcher @ http://cybersecurity.upv.es
Universitat Politècnica de València (Spain)