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Apache Tomcat: LockOutRealm treats user names as case-sensitive

High severity GitHub Reviewed Published May 12, 2026 to the GitHub Advisory Database • Updated May 18, 2026

Package

maven org.apache.tomcat.embed:tomcat-embed-core (Maven)

Affected versions

< 9.0.118
>= 10.1.0-M1, < 10.1.55
>= 11.0.0-M1, < 11.0.22

Patched versions

9.0.118
10.1.55
11.0.22
maven org.apache.tomcat:tomcat (Maven)
< 9.0.118
>= 10.1.0-M1, < 10.1.55
>= 11.0.0-M1, < 11.0.22
9.0.118
10.1.55
11.0.22
maven org.apache.tomcat:tomcat-catalina (Maven)
< 9.0.118
>= 10.1.0-M1, < 10.1.55
>= 11.0.0-M1, < 11.0.22
9.0.118
10.1.55
11.0.22

Description

Improper Handling of Case Sensitivity vulnerability in LockOutRealm in Apache Tomcat.

This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.21, from 10.1.0-M1 through 10.1.54, from 9.0.0.M1 through 9.0.117, from 8.5.0 through 8.5.100, from 7.0.0 through 7.0.109.
Older unsupported versions may also be affected.

Users are recommended to upgrade to version 11.0.22, 10.1.55 or 9.0.118 which fix the issue.

References

Published by the National Vulnerability Database May 12, 2026
Published to the GitHub Advisory Database May 12, 2026
Reviewed May 18, 2026
Last updated May 18, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(24th percentile)

Weaknesses

Improper Handling of Case Sensitivity

The product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results. Learn more on MITRE.

CVE ID

CVE-2026-43513

GHSA ID

GHSA-5mp6-jrq3-r938

Source code

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