[SECURITY] CVE-2026-43513 Apache Tomcat - LockOutRealm treats user names as case-sensitive

Mark Thomas <[email protected]> Tue, 12 May 2026 16:06:47 +0100
Newsgroups gmane.comp.jakarta.tomcat.user,gmane.comp.apache.maven.announce,gmane.comp.apache.maven.announce,gmane.text.xml.xalan.devel
Message-ID <[email protected]>
CVE-2026-43513 Apache Tomcat - LockOutRealm treats user names as 
case-sensitive

Severity: Low

Vendor: The Apache Software Foundation

Versions Affected:
Apache Tomcat 11.0.0-M1 to 11.0.21
Apache Tomcat 10.1.0-M1 to 10.1.54
Apache Tomcat 9.0.0.M1 to 9.0.117
Older, unsupported versions may also be affected

Description:
The LockOut Realm treated user names as case sensitive meaning that, for 
Realms where the user name was case insensitive, the LockOut Realm was 
not as effective at blocking brute force attacks against a user's password.

Mitigation:
Users of the affected versions should apply one of the following
mitigations:
- Upgrade to Apache Tomcat 11.0.22 or later
- Upgrade to Apache Tomcat 10.1.55 or later
- Upgrade to Apache Tomcat 9.0.118 or later

History:
2026-05-12 Original advisory

References:
[1] https://tomcat.apache.org/security-11.html
[2] https://tomcat.apache.org/security-10.html
[3] https://tomcat.apache.org/security-9.html