Executive Summary

CVE-2025-71320 is a critical vulnerability in picklescan versions before 0.0.33 caused by an incomplete deny-list of disallowed functions.

The deny-list fails to block dangerous functions such as pydoc.locate and operator.methodcaller, which attackers can exploit.

By crafting malicious pickle files that use these unblocked functions, remote attackers can bypass security checks and achieve arbitrary code execution when the pickle is deserialized.

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Impact Analysis

This vulnerability allows remote attackers to execute arbitrary code on systems that deserialize malicious pickle files using vulnerable versions of picklescan.

Successful exploitation can lead to full system compromise, including unauthorized access, data manipulation, or disruption of services.

Because the vulnerability has a high severity score (CVSS 9.3/9.8), it poses a significant security risk if not mitigated.

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Detection Guidance

This vulnerability can be detected by scanning pickle files for the presence of unblocked dangerous functions such as pydoc.locate and operator.methodcaller, which are not properly denied by picklescan versions before 0.0.33.

Since picklescan is a tool designed to scan pickle files for malicious content, you can use it to detect potentially malicious pickle files. However, versions before 0.0.33 are vulnerable and may fail to detect these functions.

To detect this vulnerability on your system, you should:

• Use an updated version of picklescan (0.0.33 or later) to scan pickle files.
• Manually inspect pickle files for usage of pydoc.locate and operator.methodcaller functions, which can be done by analyzing the pickle file content or by deserializing in a controlled environment.
• Example command to scan a pickle file with picklescan (assuming updated version): picklescan suspicious_file.pkl

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Mitigation Strategies

The immediate and recommended mitigation step is to upgrade picklescan to version 0.0.33 or later, where the deny-list has been updated to block all dangerous functions from the pydoc and operator modules, including pydoc.locate and operator.methodcaller.

Additional mitigation steps include:

• Avoid deserializing pickle files from untrusted or unauthenticated sources.
• Implement additional security controls around the use of pickle deserialization, such as sandboxing or running deserialization in isolated environments.
• Review and update any custom deny-lists or security checks to ensure they block all potentially dangerous functions, ideally using wildcards to cover all functions in risky modules.

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Compliance Impact

CVE-2025-71320 allows remote attackers to achieve arbitrary code execution by bypassing security checks in picklescan due to an incomplete deny-list. This critical vulnerability can lead to unauthorized system access and data compromise.

Such unauthorized access and potential data breaches can negatively impact compliance with common standards and regulations like GDPR and HIPAA, which require strict controls to protect sensitive data and ensure system integrity.

Failure to mitigate this vulnerability could result in violations of these regulations due to exposure of personal or protected health information through exploitation of the arbitrary code execution flaw.

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