CVE-2021-43980: Apache Tomcat

Low severity, CVSS 3.7. EPSS: 2.4% chance of exploitation in the next 30 days.

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.

Affected products

• Apache Tomcat: from 8.5.0, up to and including 8.5.77; from 9.0.0, up to and including 9.0.60; from 10.0.0, up to and including 10.0.18; version 10.1.0 only
• Debian Debian Linux: version 10.0 only; version 11.0 only

Published 2022-09-28. Last modified 2026-06-17.