Apache Shiro: Brute force attack possible to determine valid user names

Observable Timing Discrepancy vulnerability in Apache Shiro.

This issue affects Apache Shiro: from 1.*, 2.* before 2.0.7.

Users are recommended to upgrade to version 2.0.7 or later, which fixes the issue.

Prior to Shiro 2.0.7, code paths for non-existent vs. existing users are different enough, that a brute-force attack may be able to tell, by timing the requests only, determine if the request failed because of a non-existent user vs. wrong password.

The most likely attack vector is a local attack only. Shiro security model  https://shiro.apache.org/security-model.html#username_enumeration  discusses this as well.

Typically, brute force attack can be mitigated at the infrastructure level.