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CRITICAL severity

CVE-2026-55276 — tomcat

CRITICAL

CVE-2026-55276 is a critical-severity (CVSS 9.1) CWE-670 vulnerability. A fix is available — see the affected versions and patch details below.

Apache Tomcat: Logged effective web.xml is incomplete

Also known asBIT-tomcat-2026-55276
Published
Jun 29, 2026
Updated
Aug 12, 2026
Affected
1 product
Patched
See advisory
Exploits
None indexed
Exploitation data as of Sep 30, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • A successful exploit gives an attacker total control of the affected component, not partial access.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-55276.

EPSS Exploitation Probability

via FIRST.org ↗
0.6%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs47th percentile — riskier than 47% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-55276 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 380,526 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Description

Always-Incorrect Control Flow Implementation vulnerability in Apache Tomcat meant that special roles and empty authorisation constraints were not included when the effective web.xml was logged.

This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.22, from 10.1.0-M1 through 10.1.55, from 9.0.0.M1 through 9.0.118, from 8.5.0 through 8.5.100. Other versions that have reached end of support may also be affected.

Users are recommended to upgrade to version 11.0.23, 10.1.56 or 9.0.119 which fixes the issue.

Affected Products

1 product · 3 configurations
Application
tomcatapache
≥ 11.0.0 && < 11.0.23
range

Detection & mitigation playbook

Vulnerability

  1. Detect

    Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).

  2. Fix

    Upgrade the affected component to the fixed release for CVE-2026-55276, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatLow

A flaw was found in Apache Tomcat. When the effective web.xml logging feature is enabled for debugging, special roles and empty authorization constraints may be omitted from the logged output. This is a logging-only issue with no runtime security impact — it only affects the accuracy of debug log output for…

Workaround published by Red Hat
This is a logging-only issue with no runtime security impact. No mitigation is required. Administrators should not rely solely on the effective web.xml debug log output to verify security constraint configuration.
Source: Red Hat security advisory for CVE-2026-55276 (CC BY 4.0)
ProductFixed inAdvisory
Red Hat Enterprise Linux 10tomcat9-1:9.0.120-1.el10_2RHSA-2026:68651
Red Hat Enterprise Linux 10.0 Extended Update Supporttomcat9-1:9.0.120-1.el10_0RHSA-2026:67163
Red Hat Enterprise Linux 8tomcat-1:9.0.120-1.el8_10RHSA-2026:68677
Red Hat Enterprise Linux 8.8 Telecommunications Update Servicetomcat-1:9.0.120-1.el8_8RHSA-2026:68680
Red Hat Enterprise Linux 9tomcat-1:9.0.120-2.el9_8RHSA-2026:68660
Red Hat Enterprise Linux 9.2 Update Services for SAP Solutionstomcat-1:9.0.120-1.el9_2RHSA-2026:68678
Red Hat Enterprise Linux 9.4 Update Services for SAP Solutionstomcat-1:9.0.120-1.el9_4RHSA-2026:68679
Red Hat Enterprise Linux 9.6 Extended Update Supporttomcat-1:9.0.120-1.el9_6RHSA-2026:68659

Frequently Asked Questions

Always-Incorrect Control Flow Implementation vulnerability in Apache Tomcat meant that special roles and empty authorisation constraints were not included when the effective web.xml was logged. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.22, from 10.1.0-M1 through 10.1.55, from 9.0.0.M1 through 9.0.118, from 8.5.0 through 8.5.100. Other versions that have reached end of support may also be affected. Users are recommended to upgrade to version 11.0.23, 10.1.56 or 9.0.119 which fixes the issue.
O3 Security · Impact-Aware SCA

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CVE-2026-55276: tomcat (Critical 9.1) | O3 Security