dbcve.org
TomcatWeb server / proxy · Apache

CVE-2025-53506

HIGH · 7.5 CVSS v3.1 Published 2025-07-10
Fix available
A fix is available. Upgrade to after 11.0.8 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
Uncontrolled Resource Consumption vulnerability in Apache Tomcat if an HTTP/2 client did not acknowledge the initial settings frame that reduces the maximum permitted concurrent streams. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.8, from 10.1.0-M1 through 10.1.42, from 9.0.0.M1 through 9.0.106. The following versions were EOL at the time the CVE was created but are known to be affected: 8.5.0 through 8.5.100. Other EOL versions may also be affected. Users are recommended to upgrade to version 11.0.9, 10.1.43 or 9.0.107, 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

Uncontrolled resource consumption vulnerability in Apache Tomcat's HTTP/2 implementation occurs when a client sends a SETTINGS frame that reduces the maximum concurrent streams but fails to acknowledge it. Without proper acknowledgment handling, Tomcat does not release the associated resources, allowing an attacker to exhaust server resources by opening multiple malicious HTTP/2 connections.

MitigationUpgrade to Apache Tomcat 11.0.9, 10.1.43, or 9.0.107 (or later) which fix the HTTP/2 settings acknowledgment handling. If upgrade is not immediately possible, consider restricting or disabling HTTP/2 if not required.

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:>= 9.0.0, <= 9.0.106>= 10.1.0, <= 10.1.42>= 11.0.0, <= 11.0.8

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
None
Integrity
None
Availability
High

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

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 version
    Check the Tomcat installation for the version marker file (e.g., RELEASE-NOTE file in the Tomcat home directory) or examine the banner output when starting Tomcat
    Affected if The installed version falls within 9.0.0-9.0.106, 10.1.0-10.1.42, or 11.0.0-11.0.8
  2. Confirm HTTP/2 protocol is in use
    Inspect the Tomcat connector configuration in the server configuration file to determine if the HTTP/2 protocol is enabled on any connector (look for protocol="h2" or similar HTTP/2 configuration)
    Affected if HTTP/2 is enabled on one or more connectors and the Tomcat version is in the affected range
  3. Verify connector settings
    Examine the connector configuration for any maxConcurrentStreams or similar HTTP/2 stream limit settings that control maximum concurrent streams per connection
    Affected if HTTP/2 connectors exist with stream limit configurations and the version is vulnerable

The environment is affected if Apache Tomcat version is 9.0.0-9.0.106, 10.1.0-10.1.42, or 11.0.0-11.0.8 AND HTTP/2 protocol is enabled on any connector.

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 a release after 11.0.8
Interim mitigation

Upgrade to Apache Tomcat 11.0.9, 10.1.43, or 9.0.107 (or later) which fix the HTTP/2 settings acknowledgment handling. If upgrade is not immediately possible, consider restricting or disabling HTTP/2 if not required.

Recommended fix High confidence

9.0.107 (for 9.0.x), 10.1.43 (for 10.1.x), or 11.0.9 (for 11.x)

  1. Identify your current Apache Tomcat version (9.x, 10.1.x, or 11.x)
  2. Download the corresponding fixed release: 9.0.107 for 9.0.x, 10.1.43 for 10.1.x, or 11.0.9 for 11.x
  3. Stop the Tomcat service
  4. Back up your existing Tomcat installation including configuration files
  5. Replace or upgrade the Tomcat binaries with the new version
  6. Restore your configuration files from the backup (or migrate settings to the new version)
  7. Start the Tomcat service
  8. Verify the HTTP/2 endpoint is functioning correctly and the vulnerability is resolved
Caveat Patch releases typically have minimal breaking changes; review the release notes for the specific version for any configuration or behavioral changes

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

Fix this in Tomcat Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,390
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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-2025-53506 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