CVE-2026-23901: Apache Shiro: Brute force attack possible to determine valid user names

[Lenny Primak <lprimak () apache org>]

Severity: low 

Affected versions:

- Apache Shiro (org.apache.shiro:shiro-core) before 2.0.7

Description:

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.

Credit:

4ra1n (finder)
Y4tacker (finder)
lprimak (remediation developer)

References:

https://shiro.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-23901