Description
An undocumented and unsafe feature in the PLY (Python Lex-Yacc) library 3.11 allows Remote Code Execution (RCE) via the `picklefile` parameter in the `yacc()` function. This parameter accepts a `.pkl` file that is deserialized with `pickle.load()` without validation. Because `pickle` allows execution of embedded code via `__reduce__()`, an attacker can achieve code execution by passing a malicious pickle file. The parameter is not mentioned in official documentation or the GitHub repository, yet it is active in the PyPI version. This introduces a stealthy backdoor and persistence risk. NOTE: A third-party states that this vulnerability should be rejected because the proof of concept does not demonstrate arbitrary code execution and fails to complete successfully.
References
www.openwall.com/lists/oss-security/2026/01/23/4
www.openwall.com/lists/oss-security/2026/01/23/5
www.openwall.com/lists/oss-security/2026/01/28/5
www.openwall.com/lists/oss-security/2026/01/29/1
www.openwall.com/lists/oss-security/2026/01/29/2
www.openwall.com/lists/oss-security/2026/01/30/1
github.com/bohmiiidd/Undocumented-RCE-in-PLY
github.com/tom025/ply_exploit_rejection
github.com/...iiidd/Undocumument_RCE_PLY-yacc-CVE-2025-56005
github.com/tom025/ply_exploit_rejection/issues/1