CVE-2025-8291 is a vulnerability in the Python Software Foundation's CPython implementation, specifically within the 'zipfile' module. The flaw pertains to the handling of the ZIP64 End of Central Directory (EOCD) Locator record, which is critical for locating the ZIP64 EOCD record in ZIP archives that exceed traditional size limits. The 'zipfile' module fails to verify the validity of the offset value specified in the ZIP64 EOCD Locator record. Instead of using the offset to locate the ZIP64 EOCD record, the module assumes that this record is the immediate predecessor in the archive. This behavior diverges from other ZIP implementations that rely on the offset value, potentially allowing an attacker to craft ZIP archives that are interpreted differently by Python's 'zipfile' module compared to other tools. Such discrepancies could be exploited to bypass integrity checks or cause inconsistent processing of archive contents, which might lead to security issues such as data tampering or logic errors in applications relying on 'zipfile' for archive extraction. The remediation introduced by the Python Software Foundation maintains backward compatibility by preserving the original behavior but adds a validation step to ensure the offset in the ZIP64 EOCD Locator matches the expected value. This fix reduces the risk of malformed ZIP archives causing inconsistent handling. The vulnerability affects all CPython versions from 0 up to and including 3.12.0. The CVSS v3.1 base score is 4.3, indicating medium severity, with an attack vector of network, low attack complexity, no privileges required, but user interaction needed, and limited impact on integrity only. No known exploits have been reported in the wild as of the publication date.

For European organizations, this vulnerability poses a moderate risk primarily related to the integrity of ZIP archive processing in Python-based applications. Since Python is widely used in software development, automation, and data processing across Europe, any application that relies on the 'zipfile' module to handle ZIP64 archives could be susceptible to inconsistent archive interpretation. This could lead to scenarios where maliciously crafted ZIP files bypass validation or cause logic errors, potentially enabling data tampering or unauthorized code execution in downstream processes. While the vulnerability does not directly affect confidentiality or availability, the integrity impact can have cascading effects, especially in environments processing untrusted ZIP files, such as web services, CI/CD pipelines, or automated data ingestion systems. European sectors with high reliance on Python, including finance, healthcare, and government, may face increased risk if they handle ZIP64 archives from untrusted sources. The lack of known exploits reduces immediate threat but does not eliminate the risk of future exploitation. Organizations failing to update Python or implement additional validation may be vulnerable to targeted attacks exploiting this flaw.

European organizations should promptly update their Python environments to versions that include the patch for CVE-2025-8291, ensuring the 'zipfile' module performs proper offset validation for ZIP64 EOCD Locator records. Where immediate updates are not feasible, organizations should implement additional validation layers for ZIP64 archives before processing them with Python, such as using external ZIP validation tools or sandboxing archive extraction processes. Security teams should audit applications and scripts that utilize the 'zipfile' module, especially those handling ZIP files from untrusted or external sources, to identify potential exposure. Incorporating anomaly detection for ZIP archive processing errors and monitoring for unusual application behavior related to ZIP handling can help detect exploitation attempts. Additionally, educating developers about the risks of relying solely on Python's 'zipfile' module for security-critical archive processing is recommended. Organizations may also consider restricting the acceptance of ZIP64 archives or enforcing strict input validation policies in workflows that process ZIP files. Finally, maintaining an up-to-date inventory of Python versions in use across the organization will facilitate timely patch management.