# CVE-2026-43513: Apache Tomcat improper case sensitivity in LockOutRealm

Source: https://junglewise.ai/threats/cve-2026-43513-apache-tomcat-improper-case-sensitivity-in-lockoutrealm  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-12. Updated: 2026-05-18  
License: CC BY 4.0 with a link back

CVE-2026-43513 · Severity: high · CVSS 7.5 · Published 2026-05-12

Apache Tomcat is a widely used web server and application container. A vulnerability in its LockOutRealm component, which is responsible for preventing brute-force login attempts, fails to handle username case sensitivity correctly. This could allow an attacker to bypass account lockout protections or potentially gain unauthorized access by manipulating the capitalization of usernames.

Technologies: [org.apache.tomcat:tomcat (Maven)](https://junglewise.ai/threats/technologies/org-apache-tomcat-tomcat), [org.apache.tomcat:tomcat-catalina (Maven)](https://junglewise.ai/threats/technologies/org-apache-tomcat-tomcat-catalina), [org.apache.tomcat.embed:tomcat-embed-core (Maven)](https://junglewise.ai/threats/technologies/org-apache-tomcat-embed-tomcat-embed-core). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven).

## Quick answers

**Is CVE-2026-43513 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-43513 being exploited in the wild.

**How severe is CVE-2026-43513?** High severity, with a CVSS score of 7.5, published 12 May 2026.

**Which products and versions are affected?** org.apache.tomcat:tomcat (Maven) ECOSYSTEM:introduced=0,fixed=9.0.118; org.apache.tomcat:tomcat-catalina (Maven) ECOSYSTEM:introduced=0,fixed=9.0.118; org.apache.tomcat.embed:tomcat-embed-core (Maven) ECOSYSTEM:introduced=0,fixed=9.0.118.

**Is there a fix for CVE-2026-43513?** Yes. org.apache.tomcat:tomcat (Maven): upgrade to 9.0.118 or later; org.apache.tomcat:tomcat-catalina (Maven): upgrade to 9.0.118 or later; org.apache.tomcat.embed:tomcat-embed-core (Maven): upgrade to 9.0.118 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-43513 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-43513?** Check whether you run org.apache.tomcat:tomcat (Maven), org.apache.tomcat:tomcat-catalina (Maven) or org.apache.tomcat.embed:tomcat-embed-core (Maven) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- org.apache.tomcat:tomcat (Maven): upgrade to 9.0.118 or later

  ```sh
  # set org.apache.tomcat:tomcat to 9.0.118 in your pom.xml or build.gradle
  ```

- org.apache.tomcat:tomcat-catalina (Maven): upgrade to 9.0.118 or later

  ```sh
  # set org.apache.tomcat:tomcat-catalina to 9.0.118 in your pom.xml or build.gradle
  ```

- org.apache.tomcat.embed:tomcat-embed-core (Maven): upgrade to 9.0.118 or later

  ```sh
  # set org.apache.tomcat.embed:tomcat-embed-core to 9.0.118 in your pom.xml or build.gradle
  ```


## Technical details

A vulnerability classified as CWE-178 (Improper Handling of Case Sensitivity) exists in the LockOutRealm component of Apache Tomcat. The component treats usernames as case-sensitive when tracking failed login attempts, which may conflict with the underlying authentication realm's behavior if that realm is case-insensitive. An unauthenticated remote attacker can exploit this by varying the case of a username to bypass lockout thresholds or potentially access accounts if the primary authentication mechanism ignores case but the lockout mechanism does not. The issue is resolved by adding a case-sensitive attribute to LockOutRealm configuration in patched versions.

## Affected products

- Apache Tomcat 11.0.0-M1 through 11.0.21, 10.1.0-M1 through 10.1.54, 9.0.0.M1 through 9.0.117, 8.5.0 through 8.5.100, 7.0.0 through 7.0.109

## Identifiers

- CVE-2026-43513
- GHSA-5mp6-jrq3-r938

## Timeline

- 2026-05-12: disclosed
- 2026-05-12: advisory
- 2026-05-18: patched: GitHub advisory updated with patch details

## References

- [https://lists.apache.org/thread/ytjcgldshj73lcnd1sh95od5hrghwogp](https://lists.apache.org/thread/ytjcgldshj73lcnd1sh95od5hrghwogp)
- [http://www.openwall.com/lists/oss-security/2026/05/12/9](http://www.openwall.com/lists/oss-security/2026/05/12/9)
- [https://github.com/apache/tomcat/commit/4a90d3fa93988c447cd5bb7482f76ff70d7f15c2](https://github.com/apache/tomcat/commit/4a90d3fa93988c447cd5bb7482f76ff70d7f15c2)
- [https://github.com/apache/tomcat/commit/6dd75beb55bd42fc5f78e929596b25018cd17717](https://github.com/apache/tomcat/commit/6dd75beb55bd42fc5f78e929596b25018cd17717)
- [https://github.com/apache/tomcat/commit/83f3e51df7b87f5f6e626951c575ded1a512e8ef](https://github.com/apache/tomcat/commit/83f3e51df7b87f5f6e626951c575ded1a512e8ef)

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