# CVE-2020-13934: Apache Tomcat denial of service via h2c connection leak

Source: https://junglewise.ai/threats/cve-2020-13934-apache-tomcat-denial-of-service-via-h2c-connection-leak  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2022-02-08. Updated: 2026-05-20  
License: CC BY 4.0 with a link back

CVE-2020-13934 · Severity: high · CVSS 7.5 · Published 2022-02-08

Apache Tomcat is a widely used web server and application container for Java-based websites. A vulnerability in how it handles certain web connections (h2c) can allow an attacker to crash the server by exhausting its memory. This results in a denial of service, making the hosted applications and websites unavailable to legitimate users.

Technologies: [org.apache.tomcat:tomcat (Maven)](https://junglewise.ai/threats/technologies/org-apache-tomcat-tomcat), [org.apache.tomcat:tomcat-coyote (Maven)](https://junglewise.ai/threats/technologies/org-apache-tomcat-tomcat-coyote). Vendors: [Apache Software Foundation](https://junglewise.ai/threats/vendors/apache-software-foundation), [Maven](https://junglewise.ai/threats/vendors/maven).

## Quick answers

**Is CVE-2020-13934 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2020-13934 being exploited in the wild.

**How severe is CVE-2020-13934?** High severity, with a CVSS score of 7.5, published 8 February 2022.

**Which products and versions are affected?** Apache Software Foundation Coyote 10.0.0-M1 to 10.0.0-M5, 9.0.0.M5 to 9.0.35, 8.5.1 to 8.5.55; org.apache.tomcat:tomcat (Maven) ECOSYSTEM:introduced=10.0.0-M1,fixed=10.0.0-M6; org.apache.tomcat:tomcat-coyote (Maven) ECOSYSTEM:introduced=10.0.0-M1,fixed=10.0.0-M6.

**Is there a fix for CVE-2020-13934?** Yes. org.apache.tomcat:tomcat (Maven): upgrade to 10.0.0-M6 or later; org.apache.tomcat:tomcat-coyote (Maven): upgrade to 10.0.0-M6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2020-13934 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2020-13934?** Check whether you run Apache Software Foundation Coyote, org.apache.tomcat:tomcat (Maven) or org.apache.tomcat:tomcat-coyote (Maven) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- org.apache.tomcat:tomcat (Maven): upgrade to 10.0.0-M6 or later

  ```sh
  # set org.apache.tomcat:tomcat to 10.0.0-M6 in your pom.xml or build.gradle
  ```

- org.apache.tomcat:tomcat-coyote (Maven): upgrade to 10.0.0-M6 or later

  ```sh
  # set org.apache.tomcat:tomcat-coyote to 10.0.0-M6 in your pom.xml or build.gradle
  ```


## Technical details

A resource leak exists in Apache Tomcat's HTTP/2 upgrade mechanism. When an h2c (HTTP/2 Cleartext) direct connection is established, the server fails to release the HTTP/1.1 processor after the protocol upgrade. An unauthenticated remote attacker can exploit this by sending a large volume of such upgrade requests, eventually triggering an OutOfMemoryException. This results in a Denial of Service (DoS) condition. The vulnerability affects versions 10.0.0-M1 to 10.0.0-M5, 9.0.0.M5 to 9.0.35, and 8.5.1 to 8.5.55. Patches are available in versions 10.0.0-M6, 9.0.36, and 8.5.56.

## Affected products

- Apache Tomcat 10.0.0-M1 to 10.0.0-M5, 9.0.0.M5 to 9.0.35, 8.5.1 to 8.5.55
- Apache Tomcat Coyote 10.0.0-M1 to 10.0.0-M5, 9.0.0.M5 to 9.0.35, 8.5.1 to 8.5.55

## Identifiers

- CVE-2020-13934
- GHSA-vf77-8h7g-gghp

## Timeline

- 2020-07-14: disclosed: NVD publication date
- 2021-04-12: advisory: GitHub reviewed the advisory
- 2022-02-08: advisory: GitHub Advisory Database publication

## References

- [https://api.github.com/users/aruneko](https://api.github.com/users/aruneko)
- [https://github.com/aruneko](https://github.com/aruneko)
- [https://api.github.com/users/aruneko/gists%7B/gist_id%7D](https://api.github.com/users/aruneko/gists%7B/gist_id%7D)
- [https://api.github.com/users/aruneko/repos](https://api.github.com/users/aruneko/repos)
- [https://avatars.githubusercontent.com/u/2957726?v=4](https://avatars.githubusercontent.com/u/2957726?v=4)
- [https://api.github.com/users/aruneko/events%7B/privacy%7D](https://api.github.com/users/aruneko/events%7B/privacy%7D)

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