CVE-2025-31672 is a medium-severity vulnerability in the Apache POI library, specifically affecting the poi-ooxml component prior to version 5.4.0. Apache POI is a widely used Java library for reading and writing Microsoft Office file formats, including OOXML formats such as XLSX, DOCX, and PPTX. These file formats are essentially ZIP archives containing multiple XML and resource files. The vulnerability arises from improper input validation when parsing these OOXML files. Malicious actors can craft OOXML files containing ZIP entries with duplicate file names and paths. Due to inconsistent handling of these duplicate entries by different products or versions of Apache POI, the data read from the file can vary depending on which duplicate entry is selected. This inconsistency can lead to integrity issues, where an application might process unexpected or malicious data, potentially causing incorrect behavior or logic flaws in applications relying on POI for document processing. The vulnerability does not directly impact confidentiality or availability but compromises data integrity. The root cause is CWE-20, improper input validation, where the library fails to reject or properly handle duplicate ZIP entries. Apache POI version 5.4.0 addresses this issue by introducing a check that throws an exception if duplicate ZIP entries are detected, preventing ambiguous parsing. No known exploits are reported in the wild as of now. The CVSS v3.1 base score is 5.3 (medium), with attack vector network, low attack complexity, no privileges or user interaction required, and impact limited to integrity. This means an attacker can remotely send a crafted OOXML file to an application using a vulnerable POI version and cause it to process manipulated data. The vulnerability is relevant for any software or service that uses Apache POI to parse or generate OOXML files, including document management systems, enterprise content management, and automated document processing pipelines.

For European organizations, this vulnerability poses a risk primarily to the integrity of document processing workflows. Organizations that rely on Apache POI for automated handling of Office documents—such as financial institutions, government agencies, legal firms, and healthcare providers—may be vulnerable to data manipulation attacks. An attacker could craft malicious OOXML files that cause applications to interpret data incorrectly, potentially leading to erroneous decisions, data corruption, or business logic bypass. Although there is no direct confidentiality or availability impact, the integrity compromise can undermine trust in document authenticity and correctness, which is critical in regulated sectors with strict compliance requirements (e.g., GDPR, financial regulations). Additionally, since the vulnerability can be exploited remotely without authentication or user interaction, it increases the attack surface for phishing campaigns or supply chain attacks where malicious documents are delivered via email or file sharing. The lack of known exploits in the wild reduces immediate risk but does not eliminate the potential for future exploitation, especially as attackers often target widely used libraries like Apache POI. Organizations using outdated versions of POI in their internal or customer-facing applications should prioritize remediation to avoid operational and reputational damage.

1. Upgrade Apache POI to version 5.4.0 or later immediately, as this version includes the fix that detects and rejects OOXML files with duplicate ZIP entries. 2. Audit all internal and third-party applications and services that utilize Apache POI for document processing to identify vulnerable versions. 3. Implement file validation and sanitization controls at the perimeter, such as email gateways and file upload filters, to detect and block suspicious OOXML files with duplicate entries or malformed ZIP structures. 4. Employ runtime monitoring and anomaly detection to flag unusual document processing behaviors that could indicate exploitation attempts. 5. Educate users and administrators about the risks of opening unsolicited or unexpected Office documents, especially from untrusted sources. 6. For critical systems, consider sandboxing document processing components to contain potential impacts of malicious files. 7. Review and update incident response plans to include scenarios involving malicious document files exploiting Apache POI vulnerabilities. 8. Coordinate with software vendors and service providers to ensure they have applied the necessary patches if they embed Apache POI in their products.