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The CVE-2024-3832 vulnerability in Fickling stems from an incomplete static analysis mechanism for detecting unsafe Python module imports within pickles. Specifically, the `unsafe_imports()` method in `fickling/fickle.py` (lines 866-884) checks imported modules against a hardcoded tuple that omits several high-risk modules. This tuple originally included modules like os, subprocess, and `sys` but failed to list ctypes, importlib, runpy, code, and multiprocessing. These omitted modules can be leveraged for arbitrary code execution; for instance, `ctypes` allows direct memory access and calling of C functions, bypassing Python’s restrictions. When a malicious pickle imports such modules—e.g., using `ctypes.pythonapi` to execute native code—Fickling’s `check_safety()` analysis incorrectly categorizes it as “LIKELY_SAFE” because the imports are not flagged. This bypasses the tool’s primary security check, enabling attackers to craft pickles that evade detection and execute arbitrary code when loaded by applications relying on Fickling for safety assessments. The vulnerability also circumvents the `NonStandardImports` analysis since `ctypes` is part of the standard library.
Platform: Fickling
Version: Prior fixed commits
Vulnerability: Static analysis bypass
Severity: Critical
date: 2024
Prediction: Patched 2024
What Undercode Say:
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python3 -c "from fickling.fickle import Pickled; from fickling.analysis import check_safety, Severity; payload = b'\x80\x04cctypes\npythonapi\n.'; pickled = Pickled.load(payload); results = check_safety(pickled); print(f'Severity: {results.severity.name}')"
Vulnerable unsafe_imports method snippet def unsafe_imports(self) -> Iterator[ast.Import | ast.ImportFrom]: for node in self.properties.imports: if node.module in ( "<strong>builtin</strong>", "<strong>builtins</strong>", "builtins", "os", "posix", "nt", "subprocess", "sys", "builtins", "socket", "pty", "marshal", "types", ): yield node
How Exploit:
Craft pickle importing ctypes/importlib/runpy/code/multiprocessing; execute via Python unpickling; bypasses Fickling detection.
Protection from this CVE:
Update Fickling version; apply commits trailofbits/fickling@9a2b3f8, etc.; audit pickle sources.
Impact:
Arbitrary code execution; confidentiality/integrity/availability compromise; security tool bypass.
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Sources:
Reported By: github.com
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