CVE-2026-54411: Medium severity Linux-PAM Linux-PAM vulnerability

Linux-PAM through 1.7.2 contains an observable timing discrepancy (CWE-208) in the pamuserdb module's plaintext-password comparison path in modules/pamuserdb/pamuserdb.c that allows a local or network-adjacent attacker able to repeatedly drive authentication through a calling service to recover the plaintext password of a target account by measuring response-timing differences. The comparison uses strncmp() (or strncasecmp() when PAMICASEARG is set) preceded by a length-equality check, so the time to reject a candidate depends on the index of the first differing byte and on whether the candidate's length matches the stored password, leaking the password length and individual prefix bytes. The vulnerable path is reached when the administrator configures pamuserdb with crypt=none, with an unrecognized crypt method, or without a crypt= argument, causing the module to store and compare credentials in plaintext.