Spring Security, versions 4.2.x up to 4.2.12, and older unsupported versions support plain text passwords using PlaintextPasswordEncoder. If an application using an affected version of Spring Security is leveraging PlaintextPasswordEncoder and a user has a null encoded password, a malicious user (or attacker) can authenticate using a password of “null”.

• Spring Security 4.2 to 4.2.12
• Older unsupported versions are also affected
• Note that Spring Security 5+ is not impacted by this vulnerability.

Users of affected versions should apply the following mitigation:

• 4.2.x users should upgrade to 4.2.13
• Older versions should upgrade to a supported branch

There are no other mitigation steps necessary.

This issue was identified and responsibly reported by Tim Büthe and Daniel Neagaru from mytaxi.