CVE-2020-13943: Infoleak

Apache Tomcat could allow a remote attacker to obtain sensitive information, caused by a flaw when HTTP/2 client exceeded the agreed maximum number of concurrent streams for a connection. By sending a specially-crafted HTTP request, an attacker could exploit this vulnerability to see the responses for unexpected resources, and use this information to launch further attacks against the affected system.

— IBM

If an HTTP/2 client connecting to Apache Tomcat 10.0.0-M1 to 10.0.0-M7, 9.0.0.M1 to 9.0.37 or 8.5.0 to 8.5.57 exceeded the agreed maximum number of concurrent streams for a connection (in violation of the HTTP/2 protocol), it was possible that a subsequent request made on that connection could contain HTTP headers - including HTTP/2 pseudo headers - from a previous request rather than the intended headers. This could lead to users seeing responses for unexpected resources.

If an HTTP/2 client exceeded the agreed maximum number of concurrent streams for a connection (in violation of the HTTP/2 protocol), it was possible that a subsequent request made on that connection could contain HTTP headers - including HTTP/2 pseudo headers - from a previous request rather than the intended headers. This could lead to users seeing responses for unexpected resources.

Upstream commits: Tomcat 10.0: https://github.com/apache/tomcat/commit/1bbc650cbc3f08d85a1ec6d803c47ae53a84f3bb Tomcat 9.0: https://github.com/apache/tomcat/commit/55911430df13f8c9998fbdee1f9716994d2db59b Tomcat 8.5: https://github.com/apache/tomcat/commit/9d7def063b47407a09a2f9202beed99f4dcb292a

Reference: http://mail-archives.apache.org/modmbox/tomcat-announce/202010.mbox/%3C2b767c6e-dcb9-5816-bd69-a3bc0771fef3%40apache.org%3E

— Red Hat