GHSA-m7j5-r2p5-c39r: picklescan: Deserialization enables RCE

### Summary Unsafe pickle deserialization allows unauthenticated attackers to perform Arbitrary File Creation. By chaining the logging.FileHandler class, an attacker can bypass RCE-focused blocklists to create empty files on the server. The vulnerability allows creating zero-byte files in arbitrary locations but does not permit overwriting or modifying existing files. ### Details The application deserializes untrusted pickle data. While RCE keywords may be blocked, the exploit abuses standard library features: logging.FileHandler: The exploit instantiates this class using its default behavior (append mode). Behavior on Existing Files: If the target file already exists, the handler opens it without modifying its content, resulting in no impact to existing data. Behavior on Non-Existent Files: If the target file does not exist, the handler creates a new zero-byte file with the specified name. ### PoC ```python import pickle class WriteFile: def __reduce__(self): from logging import FileHandler return (FileHandler, ('evil.log',)) with open("bypass_write.pkl", "wb") as f: pickle.dump(WriteFile(), f) handler = pickle.loads(pickle.dumps(WriteFile())) ``` <img width="1201" height="140" alt="313e1cfacbe700e27b6875e49808c52a" src="https://github.com/user-attachments/assets/8873bb54-0f98-41aa-8e7c-a38a245ca428" /> ### Impact This primitive can be used for Filesystem Pollution or Logic Disruption. For example, an attacker could create specific "lock files" (e.g., maintenance.lock, .lock) that the application checks for, potentially triggering a Denial of Service (DoS) or preventing the application from starting.

An adversary uploads a weaponized .pkl file to a public model hub or submits it as a 'contributed model' to an ML project. The victim's CI/CD pipeline automatically runs picklescan to validate the artifact before registering it. During scanning, picklescan deserializes the pickle payload, which instantiates logging.FileHandler and creates a zero-byte maintenance.lock file in the application working directory. On next service restart the application detects the lock file and enters a degraded maintenance mode — or refuses to start entirely — causing a production outage. The attacker achieves reliable DoS with no credentials, no network access beyond file submission, and no malware detectable in the artifact itself since logging.FileHandler is a standard library class.