PLY versions 3.2 to 3.11 include an undocumented 'picklefile' parameter in the yacc() function that accepts a .pkl file deserialized with pickle.load() without validation. Because Python's pickle deserialization can execute embedded code via __reduce__(), an attacker able to control the pickle file can execute arbitrary code on the affected system. This vulnerability is not documented in official PLY documentation or GitHub but is present in the PyPI-distributed versions. Exploitation requires the application to explicitly implement this parameter and depends on the attacker's ability to influence the pickle file loaded, such as through shared directory race conditions, configuration injection, supply chain compromise, or chaining with other vulnerabilities. Red Hat classifies this as an Important severity issue due to its limited attack surface and conditional exploitability.

If exploited, an attacker can execute arbitrary code on the affected system during the deserialization of a malicious pickle file. This can lead to full compromise of the application environment, including modification of application data, unauthorized actions, and potential denial of service. However, exploitation requires specific conditions: the application must explicitly use the undocumented 'picklefile' parameter, and the attacker must control or influence the pickle file loaded. Therefore, the impact is significant but limited to contexts where these conditions are met.

Red Hat has not indicated an official patch or fix currently available for this vulnerability. Mitigation involves ensuring that applications do not use the undocumented 'picklefile' parameter or do not load pickle files from untrusted sources. Since exploitation requires the attacker to influence the pickle file, preventing untrusted file injection or modification is critical. Monitor vendor advisories for updates or patches. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance.