REDHAT-BUG-2319212: Medium severity Linux-PAM PAM vulnerability

A vulnerability was found in PAM. The secret is in memory, while the attacker can trigger the victim program to execute by sending characters to its stdin. In-between, they then train the branch predictor to speculatively execute a ROP chain.

Moreover, when stdin is a pipe or file, the FILE IO buffer malloc'd will receive the just-freed IO buffer that was used to read /etc/shadow, so it is also possible to have the secret conveniently available in the uninitialized memory of the stdin's FILE buf.=20

This makes several registers reference the /etc/shadow contents during the read-loop of the fgets call that the polkit agent uses in the pam conversation.=20

The attack is difficult to pull of: - Attacker needs to find a gadget chain in the mapped-in executable memory of the victim - Attacker needs to trigger TLB entries to be prefetched to win the race and fit the transient operations in the misspeculation window. - Attacker needs to tweak the attack to break ASLR. This they also can do using Spectre as well.