A deserialization flaw was discovered in Apache Tomcat's use of a FileStore. An attacker can exploit the flaw if all of the following are true: An attacker is able to control the contents and name of a file on the server. The server is configured to use the PersistenceManager with a FileStore. The PersistenceManager is configured with sessionAttributeValueClassNameFilter="null" (the default unless a SecurityManager is used) or a sufficiently lax filter to allow the attacker-provided object to be deserialized. The attacker knows the relative file path from the storage location used by FileStore to the file the attacker has control over. If all these conditions are true, the attacker can use a specifically crafted request to trigger Remote Code Execution through deserialization of the file under their control.

This flaw affects the following Tomcat versions: 10.0.0-M1 to 10.0.0-M4, 9.0.0.M1 to 9.0.34, 8.5.0 to 8.5.54, and 7.0.0 to 7.0.103.

Upstream commits:

Tomcat 10.0: https://github.com/apache/tomcat/commit/bb33048e3f9b4f2b70e4da2e6c4e34ca89023b1b Tomcat 9.0: https://github.com/apache/tomcat/commit/3aa8f28db7efb311cdd1b6fe15a9cd3b167a2222 Tomcat 8.5: https://github.com/apache/tomcat/commit/ec08af18d0f9ddca3f2d800ef66fe7fd20afef2f Tomcat 7.0: https://github.com/apache/tomcat/commit/53e30390943c18fca0c9e57dbcc14f1c623cfd06

Fixed bug (OOB Read in urldecode()). (CVE-2020-7067)