The ExecShield feature in a certain Red Hat patch for the Linux kernel in Red Hat Enterprise Linux (RHEL) 5 and 6 and Fedora 15 and 16 does not properly handle use of many shared libraries by a 32-bit executable file, which makes it easier for context-dependent attackers to bypass the ASLR protection mechanism by leveraging a predictable base address for one of these libraries.
https://oss.oracle.com/git/?p=redpatch.git%3Ba=commit%3Bh=302a4fc15aebf202b6dffd6c804377c6058ee6e4
https://bugzilla.redhat.com/show_bug.cgi?id=804947
http://www.openwall.com/lists/oss-security/2012/03/20/4
http://scarybeastsecurity.blogspot.com/2012/03/some-random-observations-on-linux-aslr.html