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.

xlockmore and xlockf do not properly cleanse user-injected format strings, which allows local users to gain root privileges via the -d option.

Buffer overflow in xlockmore xlock program version 4.16 and earlier allows local users to read sensitive data from memory via a long -mode option.