Pluggable Authentication Modules
Where this stands
One published detection covers this technique. Every one is unverified — no rule on Siemphony has been executed against real telemetry.
What the technique is
Adversaries may modify pluggable authentication modules (PAM) to access user credentials or enable otherwise unwarranted access to accounts. PAM is a modular system of configuration files, libraries, and executable files which guide authentication for many services. The most common authentication module is pam_unix.so, which retrieves, sets, and verifies account authentication information in /etc/passwd and /etc/shadow. Adversaries may modify components of the PAM system to create backdoors. PAM components, such as pam_unix.so, can be patched to accept arbitrary adversary supplied values as legitimate credentials. Malicious modifications to the PAM system may also be abused to steal credentials. Adversaries may infect PAM resources with code to harvest user credentials, since the values exchanged with PAM components may be plain-text since PAM does not store passwords.
Read it on attack.mitre.orgWhat MITRE says you would watch
- AN1250
Detects unauthorized modifications to PAM configuration files or shared object modules. Correlates file modification events under /etc/pam.d/ or /lib/security/ with unusual authentication activity such as multiple simultaneous logins, off-hours logins, or logons without corresponding physical/VPN access.
- AN1251
Detects suspicious changes to macOS authorization and PAM plugin files. Correlates file modifications under /etc/pam.d/ or /Library/Security/SecurityAgentPlugins with unexpected authentication attempts or anomalous account usage.
Technique names and descriptions © MITRE ATT&CK®, CC BY 4.0. Not endorsed by MITRE.