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TomcatWeb server / proxy · Apache

CVE-2026-34483

HIGH · 7.5 CVSS v3.1 Published 2026-04-09
Fix available
A fix is available. Upgrade to 9.0.117 / 10.1.54 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 Encoding or Escaping of Output vulnerability in the JsonAccessLogValve component of Apache Tomcat. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.20, from 10.1.0-M1 through 10.1.53, from 9.0.40 through 9.0.116. Users are recommended to upgrade to version 11.0.21, 10.1.54 or 9.0.117 , 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 · high confidence

The JsonAccessLogValve component in Apache Tomcat fails to properly encode or escape output when generating JSON-formatted access logs. This improper encoding could allow attackers to inject malicious content into log files, potentially leading to log injection, JSON parsing bypass, or secondary attack vectors if logs are viewed in web interfaces.

MitigationUpgrade Apache Tomcat to version 11.0.21, 10.1.54, or 9.0.117 to obtain the patched version of JsonAccessLogValve that properly encodes output.

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:>= 9.0.40, < 9.0.117>= 10.1.0, < 10.1.54>= 11.0.0, < 11.0.21

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 Apache Tomcat installation and version
    Check for Tomcat by locating the catalina.jar file (typically in the lib directory) or by running the version.sh/version.bat script in the bin directory. The version is typically printed in the output.
    Affected if The installed version falls within the affected ranges: 9.0.40 to 9.0.116, 10.1.0 to 10.1.53, or 11.0.0 to 11.0.20
  2. Locate Tomcat configuration files
    Navigate to the Tomcat conf directory and identify server.xml and context.xml files. These files contain Valve configurations that control access logging behavior.
    Affected if Configuration files exist and are accessible for inspection
  3. Check if JsonAccessLogValve is configured
    Search server.xml and context.xml for the string 'JsonAccessLogValve' or look for Valve definitions with className containing 'JsonAccessLogValve'. This valve generates JSON-formatted access logs.
    Affected if A Valve with className set to org.apache.catalina.valves.JsonAccessLogValve is present in the configuration
  4. Verify JSON access logging is enabled
    Examine the Valve configuration found in the previous step. Confirm that the JsonAccessLogValve is not commented out and is actively enabled for access logging.
    Affected if The JsonAccessLogValve is uncommented and active in the configuration, meaning JSON-formatted access logs are being generated

A system is affected if it runs Apache Tomcat version 9.0.40-9.0.116, 10.1.0-10.1.53, or 11.0.0-11.0.20 AND has the JsonAccessLogValve configured and enabled for generating JSON-formatted access logs.

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 9.0.117 / 10.1.54 / 11.0.21 or later
Fixed in 9.0.11710.1.5411.0.21
Interim mitigation

Upgrade Apache Tomcat to version 11.0.21, 10.1.54, or 9.0.117 to obtain the patched version of JsonAccessLogValve that properly encodes output.

Recommended fix High confidence

Apache Tomcat 9.0.117, 10.1.54, or 11.0.21 depending on your current version branch

  1. Identify your current Tomcat major version line (9.x, 10.1.x, or 11.x) by checking the version string in the server info
  2. Stop the Tomcat service or instance
  3. Create a complete backup of your existing Tomcat installation directory including all configuration files, web applications, and libraries
  4. Download the appropriate fixed version from the official Apache Tomcat mirror: 9.0.117 for 9.x users, 10.1.54 for 10.1.x users, or 11.0.21 for 11.x users
  5. Extract the new Tomcat version to a temporary location
  6. Copy or migrate your configuration files (server.xml, context.xml, etc.) from the backup to the new installation
  7. Deploy your web applications to the new installation
  8. Start the Tomcat service and verify the server starts successfully
Caveat Minor: Review release notes for any changes in default behavior or deprecated features between your version and the fixed release

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
  • Testing8.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,680
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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-2026-34483 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data