Passing an absolute path to a file_exists check in phpBB before 3.2.4 allows Remote Code Execution through Object Injection by employing Phar deserialization when an attacker has access to the Admin Control Panel with founder permissions.
Weakness
The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Phpbb | Phpbb | * | 3.2.4 (excluding) |
| Phpbb3 | Ubuntu | esm-apps/xenial | * |
| Phpbb3 | Ubuntu | esm-infra-legacy/trusty | * |
| Phpbb3 | Ubuntu | trusty | * |
| Phpbb3 | Ubuntu | trusty/esm | * |
| Phpbb3 | Ubuntu | upstream | * |
| Phpbb3 | Ubuntu | xenial | * |
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.
Related Attack Patterns
References
- https://blog.ripstech.com/2018/phpbb3-phar-deserialization-to-remote-code-execution/
- https://lists.debian.org/debian-lts-announce/2018/11/msg00029.html
- https://www.phpbb.com/community/viewtopic.php?f=14\u0026t=2492206
- https://blog.ripstech.com/2018/phpbb3-phar-deserialization-to-remote-code-execution/
- https://lists.debian.org/debian-lts-announce/2018/11/msg00029.html
- https://www.phpbb.com/community/viewtopic.php?f=14\u0026t=2492206