CVE-2021-43980

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.