CVE-2021-30639: Apache Tomcat

High severity, CVSS 7.5. EPSS: 6.9% chance of exploitation in the next 30 days.

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.

Affected products

• Apache Tomcat: version 8.5.64 only; version 9.0.44 only; version 10.0.3 only; version 10.0.4 only
• McAfee Epolicy Orchestrator: before 5.10.0 (fixed in 5.10.0); version 5.10.0 only
• Oracle Big Data Spatial And Graph: before 23.1 (fixed in 23.1)

Published 2021-07-12. Last modified 2026-06-17.