CVE-2025-59232 is an out-of-bounds read vulnerability classified under CWE-125 affecting Microsoft Office Online Server, specifically its Excel processing component. This vulnerability arises when the software improperly reads memory outside the intended buffer boundaries during Excel file handling, leading to potential disclosure of sensitive information stored in adjacent memory locations. The flaw can be triggered by an unauthorized attacker with local access who persuades a user to interact with a crafted Excel file or component within the Office Online Server environment. The vulnerability does not require any privileges (PR:N) but does require user interaction (UI:R), and the attack vector is local (AV:L), meaning the attacker must have access to the system or environment where Office Online Server is running. The impact is high on confidentiality (C:H) due to information disclosure and high on availability (A:H) because the out-of-bounds read could cause application crashes or instability. Integrity is not impacted (I:N). The vulnerability affects version 16.0.0.0 of Office Online Server. Although no exploits are currently known in the wild, the vulnerability's characteristics suggest that exploitation could lead to sensitive data leakage and service disruption. The CVSS v3.1 base score is 7.1, reflecting the significant risk posed by this vulnerability. The lack of a patch at the time of publication means organizations must rely on mitigation strategies until an official fix is released.

For European organizations, this vulnerability poses a significant risk to confidentiality and availability of data processed through Microsoft Office Online Server, particularly Excel files. Sensitive information could be exposed locally, which is critical for organizations handling personal data under GDPR regulations. The potential for application crashes could disrupt business operations, especially in environments relying heavily on Office Online Server for collaborative document editing and processing. Organizations in sectors such as finance, healthcare, government, and critical infrastructure are particularly vulnerable due to the sensitivity of their data and the reliance on Microsoft Office services. The local attack vector limits remote exploitation but insider threats or compromised internal systems could leverage this vulnerability. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits post-disclosure. The impact on availability could also affect service continuity, leading to operational downtime and potential regulatory non-compliance.

1. Restrict local access to systems running Microsoft Office Online Server to trusted personnel only, minimizing the risk of unauthorized local exploitation. 2. Implement strict user access controls and monitoring to detect unusual activities that could indicate exploitation attempts. 3. Educate users and administrators about the risks of opening or interacting with untrusted Excel files within the Office Online Server environment. 4. Employ application whitelisting and endpoint protection solutions that can detect anomalous behavior related to memory access violations. 5. Monitor official Microsoft channels for patches or updates addressing CVE-2025-59232 and apply them promptly once available. 6. Consider isolating Office Online Server instances in segmented network zones to limit lateral movement in case of compromise. 7. Conduct regular security audits and vulnerability assessments focusing on Office Online Server deployments. 8. Use logging and alerting mechanisms to capture and respond to crashes or abnormal application behavior that could indicate exploitation attempts.