dbcve.org
TomcatWeb server / proxy · Apache

CVE-2026-43513

HIGH · 7.5 CVSS v3.1 Published 2026-05-12
Fix available
A fix is available. Upgrade to 9.0.118 / 10.1.55 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

The LockOutRealm component in Apache Tomcat, which provides account lockout functionality to prevent brute-force attacks, improperly handles case sensitivity when checking usernames. This could allow an attacker to bypass lockout protections by using different letter casing (e.g., 'Admin' vs 'admin') to continue brute-force attempts after an account is locked.

MitigationUpgrade Apache Tomcat to version 11.0.22, 10.1.55, or 9.0.118 (depending on the major version line in use) to obtain the fix for the case sensitivity handling flaw in LockOutRealm.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
TomcatWeb server / proxy
Affected:>= 7.0.0, <= 7.0.109>= 8.5.0, <= 8.5.100>= 9.0.0, < 9.0.118>= 10.1.0, < 10.1.55>= 11.0.0, < 11.0.22

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Tomcat installation version
    Locate the catalina.jar file in the Tomcat lib directory and read its META-INF/MANIFEST.MF file, or execute the version.sh script in the Tomcat bin directory. Look for the Specification-Version or Tomcat version number.
    Affected if The version falls within any of these ranges: 7.0.0 to 7.0.109, 8.5.0 to 8.5.100, 9.0.0 to 9.0.117, 10.1.0 to 10.1.54, or 11.0.0 to 11.0.21
  2. Confirm LockOutRealm is in use
    Examine the conf/server.xml and conf/context.xml files for a <Realm> element. Look for a className attribute containing 'LockOutRealm', for example: <Realm className='org.apache.catalina.realm.LockOutRealm' .../>
    Affected if LockOutRealm is configured as the authentication realm in server.xml or context.xml
  3. Check for nested Realms beneath LockOutRealm
    Within the same Realm element in server.xml or context.xml, inspect child elements that define the underlying user database such as <UserDatabase>, <DataSourceRealm>, <JDBCRealm>, or <MemoryRealm>. Note the username storage format used.
    Affected if LockOutRealm wraps another Realm and usernames are stored in a case-sensitive format, making the bypass possible

You are affected if your Tomcat version is within the affected ranges AND LockOutRealm is configured as your authentication realm, allowing case-variant username attempts to bypass lockout protections.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 9.0.118 / 10.1.55 / 11.0.22 or later
Fixed in 9.0.11810.1.5511.0.22
Interim mitigation

Upgrade Apache Tomcat to version 11.0.22, 10.1.55, or 9.0.118 (depending on the major version line in use) to obtain the fix for the case sensitivity handling flaw in LockOutRealm.

Recommended fix High confidence

Tomcat 9.0.118 (or 10.1.55/11.0.22 depending on your major version line)

  1. Identify your current Apache Tomcat version by checking the $CATALINA_HOME/lib/catalina.jar or server info
  2. For Tomcat 7.x (7.0.0-7.0.109): This version line is end-of-life with no direct fix; migrate to Tomcat 9.x or 10.x/11.x
  3. For Tomcat 8.5.x (8.5.0-8.5.100): Upgrade to Tomcat 9.0.118 or later, or Tomcat 10.1.x/11.x
  4. For Tomcat 9.0.x (9.0.0-9.0.117): Upgrade to version 9.0.118
  5. For Tomcat 10.1.x (10.1.0-10.1.54): Upgrade to version 10.1.55
  6. Download the new version from https://tomcat.apache.org/
  7. Stop the Tomcat service or instance
  8. Backup your existing Tomcat installation including conf/ directory
Caveat Review release notes for breaking changes between versions; minor version upgrades typically have low risk but configuration changes may be needed

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Tomcat Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-43513 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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