From secunia advisory at $URL:
A vulnerability has been discovered in mcrypt, which can be exploited by malicious people to compromise a user's system.
The vulnerability is caused due to a boundary error in the "check_file_head()" function (src/extra.c) when processing the header of an encrypted file and can be exploited to cause a stack-based buffer overflow.
Successful exploitation may allow execution of arbitrary code, but requires tricking a user into decrypting a malicious file.
The vulnerability is confirmed in version 2.6.8. Other versions may also be affected.
No official solution is currently available.
Just in case, there is a preliminary patch: http://www.openwall.com/lists/oss-security/2012/09/06/8
Stack-based buffer overflow in the check_file_head function in extra.c in
mcrypt 2.6.8 and earlier allows user-assisted remote attackers to execute
arbitrary code via an encrypted file with a crafted header containing long
salt data that is not properly handled during decryption.
Fixed in mcrypt-2.6.8-r2
New GLSA request filed.
This issue was resolved and addressed in
GLSA 201405-19 at http://security.gentoo.org/glsa/glsa-201405-19.xml
by GLSA coordinator Sean Amoss (ackle).