dbcve.org
TomcatWeb server / proxy · Apache

CVE-2020-11996

HIGH · 7.5 CVSS v3.1 Published 2020-06-26
Fix available
A fix is available. Upgrade to after 20.12 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
A specially crafted sequence of HTTP/2 requests sent to Apache Tomcat 10.0.0-M1 to 10.0.0-M5, 9.0.0.M1 to 9.0.35 and 8.5.0 to 8.5.55 could trigger high CPU usage for several seconds. If a sufficient number of such requests were made on concurrent HTTP/2 connections, the server could become unresponsive.

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

A vulnerability in Apache Tomcat's HTTP/2 implementation allows specially crafted sequences of HTTP/2 requests to cause high CPU usage. With sufficient concurrent connections sending these requests, the server can become completely unresponsive, resulting in a Denial of Service condition.

MitigationUpgrade to Tomcat 10.0.0-M6 or later, 9.0.36 or later, or 8.5.56 or later to patch the HTTP/2 request handling code.

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:>= 8.5.0, <= 8.5.55>= 9.0.0, <= 9.0.35= 9.0.0= 10.0.0
Ubuntu LinuxOperating system
Affected:= 20.04
Debian LinuxOperating system
Affected:= 9.0= 10.0
Mysql Enterprise MonitorDatabase / datastore
Affected:<= 8.0.21
Siebel Ui FrameworkApplication
Affected:<= 20.12
Workload ManagerApplication
Affected:= 12.2.0.1= 18c= 19c
LeapOperating system
Affected:= 15.1= 15.2
Oncommand System ManagerApplication
Affected:= 3.0= 3.1.3

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 Tomcat installation and version
    Locate the Tomcat installation directory (commonly in /opt/tomcat, /usr/share/tomcat, or a vendor-specific path). Check the version by reading the RELEASE-NOTES file or the lib/catalina.jar manifest, or run: java -cp lib/catalina.jar org.apache.catalina.util.ServerInfo
    Affected if The installed version is 8.5.0 through 8.5.55, 9.0.0 through 9.0.35, or specifically 9.0.0 or 10.0.0
  2. Locate and inspect server.xml
    Find the server.xml configuration file (typically in the conf/ directory of the Tomcat installation). Open it and search for <Connector> elements with the protocol attribute set to HTTP/2 (org.apache.coyote.http2.Http2Protocol) or check for any HTTP/2 upgrade configuration.
    Affected if An HTTP/2 connector is defined and enabled in server.xml
  3. Verify HTTP/2 upgrade mechanism is configured
    In server.xml, check <Connector> definitions for the upgradeProtocol attribute set to org.apache.coyote.http2.Http2Protocol, or verify if HTTP/2 is enabled via the default protocol configuration that supports upgrade to HTTP/2.
    Affected if HTTP/2 upgrade or protocol is configured on any connector
  4. Confirm the server is exposed to network requests
    Verify the Tomcat server is reachable over the network on its configured HTTP/HTTPS ports. Check if the application exposes HTTP/2 endpoints to clients or is behind a load balancer using HTTP/2.
    Affected if The server accepts external HTTP/2 connections

You are affected if your environment runs a vulnerable Apache Tomcat version (8.5.0-8.5.55, 9.0.0-9.0.35, or 9.0.0/10.0.0 specifically) with an HTTP/2 connector enabled and accessible over the network.

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.

From vendor data
Upgrade available Upgrade to a release after 20.12
Interim mitigation

Upgrade to Tomcat 10.0.0-M6 or later, 9.0.36 or later, or 8.5.56 or later to patch the HTTP/2 request handling code.

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
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,328.

Scan for this in your stack

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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-2020-11996 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