Critical Vulnerability in Python PLY Library Enables Remote Code Execution \u2013 PoC Published
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A critical vulnerability has been identified in the PyPI-distributed version of PLY (Python Lex-Yacc) 3.11, allowing arbitrary code execution through unsafe deserialization<\/a> of untrusted pickle files.<\/p>\n The vulnerability, assigned CVE-2025-56005, affects the undocumented\u00a0picklefile\u00a0parameter in the\u00a0yacc()\u00a0function, which remains absent from official documentation despite being present in the production release.<\/p>\n The vulnerability stems from the\u00a0yacc(picklefile=\u2026)\u00a0parameter invoking\u00a0pickle.load()\u00a0on attacker-controlled files without validation.<\/p>\n Python\u2019s pickle module inherently supports arbitrary code execution during deserialization through the\u00a0__reduce__()\u00a0method, enabling malicious payloads<\/a> to execute system commands before parser initialization occurs.<\/p>\n This presents a unique risk profile because the code execution happens silently during application startup, before any parsing logic is reached.<\/p>\n The vulnerability is particularly dangerous in environments where parser tables are cached on disk, shared between services, or generated in CI\/CD pipelines<\/a>.<\/p>\n Exploitation becomes possible when attackers can control, replace, or influence the pickle file path, such as:<\/p>\n