The (1) checkPasswd and (2) checkGroupXlockPasswds functions in xlockmore before 5.43 do not properly handle when a NULL value is returned upon an error by the crypt or dispcrypt function as implemented in glibc 2.17 and later, which allows attackers to bypass the screen lock via vectors related to invalid salts.
Gentoo Linux Security Advisory 201309-3 - A buffer overflow in Xlockmore might allow remote attackers to cause a Denial of Service. Versions less than 5.43 are affected.