CVE-2025-64403 is a missing authorization vulnerability (CWE-862) in Apache OpenOffice Calc, a component of the Apache OpenOffice suite widely used for spreadsheet processing. The vulnerability arises because Calc spreadsheets can include links to external data sources, which are intended to be loaded with user consent. However, due to insufficient authorization checks, an attacker can craft a malicious spreadsheet document that contains external data source links which are loaded automatically upon opening the document without any prompt or user authorization. This behavior can be exploited by attackers to exfiltrate sensitive data or manipulate data integrity by fetching or injecting malicious content from external sources. The vulnerability affects all Apache OpenOffice versions up to and including 4.1.15. The CVSS v3.1 base score is 8.1, indicating a high severity level, with an attack vector of network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), but requiring user interaction (UI:R). The impact on confidentiality and integrity is high, while availability is not affected. No known exploits are reported in the wild as of the publication date. The Apache Software Foundation has addressed this issue in version 4.1.16, recommending users upgrade promptly. This vulnerability is particularly concerning because it bypasses expected user authorization prompts, increasing the risk of stealthy data compromise.

For European organizations, the impact of CVE-2025-64403 can be significant, especially in sectors that rely heavily on Apache OpenOffice for document creation and data analysis, such as government agencies, educational institutions, and public administration. The automatic loading of external data sources without user consent can lead to unauthorized disclosure of sensitive information, including internal network details or confidential data referenced in spreadsheets. Additionally, attackers could manipulate data integrity by injecting malicious external content, potentially affecting decision-making processes or financial calculations. Since the vulnerability requires user interaction (opening a malicious document), phishing or social engineering campaigns could be used to deliver the exploit. The widespread use of Apache OpenOffice in Europe, particularly in organizations favoring open-source solutions, increases the attack surface. Unpatched systems could face data breaches, loss of trust, and compliance violations under GDPR due to unauthorized data access. Although no active exploits are known, the high CVSS score and ease of exploitation warrant urgent mitigation to prevent future attacks.

To mitigate CVE-2025-64403, European organizations should immediately upgrade all Apache OpenOffice installations to version 4.1.16 or later, which contains the fix for the missing authorization issue. Until upgrades are completed, organizations should implement strict document handling policies, including disabling automatic loading of external data sources in Calc if configurable. User awareness training should emphasize the risks of opening spreadsheet documents from untrusted or unknown sources to reduce the likelihood of successful phishing attacks. Network-level controls such as blocking or monitoring outbound connections to untrusted external data sources referenced in documents can help detect or prevent exploitation attempts. Organizations should also audit and restrict the use of Apache OpenOffice in high-risk environments and consider alternative office suites with stronger security controls if feasible. Regular vulnerability scanning and patch management processes must be enforced to ensure timely application of security updates. Finally, monitoring for unusual network activity or data exfiltration attempts related to document processing can provide early detection of exploitation attempts.