The PTR_MANGLE implementation in the GNU C Library (aka glibc or libc6) 2.4, 2.17, and earlier, and Embedded GLIBC (EGLIBC) does not initialize the random value for the pointer guard, which makes it easier for context-dependent attackers to control execution flow by leveraging a buffer-overflow vulnerability in an application and using the known zero value pointer guard to calculate a pointer address.
http://hmarco.org/bugs/CVE-2013-4788.html
http://seclists.org/fulldisclosure/2015/Sep/23
http://www.mandriva.com/security/advisories?name=MDVSA-2013:283
http://www.mandriva.com/security/advisories?name=MDVSA-2013:284
http://www.openwall.com/lists/oss-security/2013/07/15/9