It was discovered that the fix for CVE-2020-9484 was incomplete. When using Apache Tomcat with a configuration edge case that was highly unlikely to be used, the Tomcat instance was still vulnerable to CVE-2020-9484. Note that both the previously published prerequisites for CVE-2020-9484 and the previously published mitigations for CVE-2020-9484 also apply to this issue.
For reference the original advisory text follows.
When using Apache Tomcat if a) an attacker is able to control the contents and name of a file on the server; and b) the server is configured to use the PersistenceManager with a FileStore; and c) 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; and d) the attacker knows the relative file path from the storage location used by FileStore to the file the attacker has control over; then, using a specifically crafted request, the attacker will be able to trigger remote code execution via deserialization of the file under their control. Note that all of conditions a) to d) must be true for the attack to succeed.
For Debian 8 jessie, these problems have been fixed in version 7.0.56-3+really7.0.100-1+deb8u3.
We recommend that you upgrade your tomcat7 packages.
Further information about Extended LTS security advisories can be found at: debian Extended Long term support