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.