In Trail of Bits fickling versions up to and including 0.1.11, the UnsafeImportsML analysis pass unconditionally calls AnalysisContext.shorten_code(node) on every import node it inspects, regardless of whether the import is flagged as unsafe. This call registers the shortened code representation in the shared AnalysisContext.reported_shortened_code set. When the MLAllowlist analysis pass subsequently runs, it calls the same shorten_code() method, receives already_reported=True for every import, and executes a continue statement that skips its allowlist check entirely. This renders MLAllowlist dead code for all imports — it never evaluates whether an import is in the ML allowlist or not. The MLAllowlist pass was designed to catch imports of modules outside the known-safe ML ecosystem (torch, numpy, transformers, etc.) that slip past the UnsafeImports denylist. With MLAllowlist inoperative, any standard library module not in the UNSAFE_IMPORTS denylist can be invoked via pickle deserialization while ficklings check_safety() returns LIKELY_SAFE. The fickling.load() API chains check_safety() into pickle.loads() as an explicit security gate, meaning a LIKELY_SAFE verdict causes the payload to be deserialized and executed. The root cause is shared mutable state between independently-correct analysis passes — UnsafeImportsML works as designed in isolation, MLAllowlist works as designed in isolation, but the shared reported_shortened_code set causes UnsafeImportsML to poison MLAllowlists deduplication logic.
Weakness
The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Fickling | Trailofbits | * | 0.1.11 (including) |
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/1.html
- https://cwe.mitre.org/data/definitions/107.html
- https://cwe.mitre.org/data/definitions/127.html
- https://cwe.mitre.org/data/definitions/17.html
- https://cwe.mitre.org/data/definitions/20.html
- https://cwe.mitre.org/data/definitions/22.html
- https://cwe.mitre.org/data/definitions/237.html
- https://cwe.mitre.org/data/definitions/36.html
- https://cwe.mitre.org/data/definitions/477.html
- https://cwe.mitre.org/data/definitions/480.html
- https://cwe.mitre.org/data/definitions/51.html
- https://cwe.mitre.org/data/definitions/57.html
- https://cwe.mitre.org/data/definitions/59.html
- https://cwe.mitre.org/data/definitions/65.html
- https://cwe.mitre.org/data/definitions/668.html
- https://cwe.mitre.org/data/definitions/74.html
- https://cwe.mitre.org/data/definitions/87.html
References
- https://github.com/trailofbits/fickling/commit/41ce7cb01edd97072994039574a2301ebb3f463d
- https://github.com/trailofbits/fickling/pull/278
- https://github.com/trailofbits/fickling/releases/tag/v0.1.12
- https://github.com/trailofbits/fickling/security/advisories/GHSA-cffv-grgg-g429
- https://github.com/trailofbits/fickling/security/advisories/GHSA-cffv-grgg-g429