The extension fails to properly define allowed classes used when deserializing transport failure metadata. An attacker may exploit this to execute untrusted serialized code. Note that an active exploit requires write access to the directory configured at $GLOBALS[TYPO3_CONF_VARS][MAIL][transport_spool_filepath].
Weakness
The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
Potential Mitigations
- Make fields transient to protect them from deserialization.
- An attempt to serialize and then deserialize a class containing transient fields will result in NULLs where the transient data should be. This is an excellent way to prevent time, environment-based, or sensitive variables from being carried over and used improperly.