CVE-2025-20128 is a heap-based buffer overflow vulnerability located in the Object Linking and Embedding 2 (OLE2) decryption routine of ClamAV, which is integrated into Cisco Secure Endpoint. The root cause is an integer underflow in a bounds check that allows a heap buffer overflow read when processing specially crafted OLE2 content. An attacker can exploit this remotely without authentication by submitting a malicious file for scanning, causing the ClamAV process to crash and resulting in a denial of service (DoS) condition. This vulnerability affects a wide range of Cisco Secure Endpoint versions, spanning multiple major releases. The impact is limited to availability, as the exploit terminates the scanning process but does not allow code execution or data compromise. Cisco has acknowledged the vulnerability and released software updates to remediate it; however, no alternative mitigations or workarounds are available. The vulnerability has a CVSS v3.1 base score of 5.3, reflecting its medium severity due to ease of exploitation and lack of confidentiality or integrity impact. There are currently no known exploits in the wild. Organizations relying on Cisco Secure Endpoint should apply the provided patches promptly to prevent potential service disruption and maintain endpoint security posture.

For European organizations, this vulnerability primarily threatens the availability of Cisco Secure Endpoint's malware scanning capabilities. A successful exploit can cause denial of service by crashing the ClamAV scanning process, potentially leaving endpoints unprotected against malware and other threats during the downtime. This could increase the risk of secondary attacks or malware infections, especially in environments with high reliance on automated endpoint protection. Critical infrastructure, financial institutions, healthcare providers, and large enterprises using Cisco Secure Endpoint may experience operational disruptions or increased exposure to cyber threats. Although the vulnerability does not directly compromise confidentiality or integrity, the temporary loss of endpoint defense can have cascading security implications. The broad range of affected versions means many organizations may be vulnerable if patches are not applied promptly. Given the lack of workarounds, patching is the only effective mitigation to maintain continuous protection.

1. Immediately identify all instances of Cisco Secure Endpoint deployed within the organization and verify their versions against the affected list. 2. Prioritize deployment of Cisco's official patches or updates that address CVE-2025-20128 to all affected systems without delay. 3. Implement strict file upload and scanning policies to limit exposure to untrusted or suspicious OLE2 files, especially from external sources. 4. Monitor endpoint security logs and ClamAV scanning processes for abnormal terminations or crashes that could indicate attempted exploitation. 5. Employ network segmentation and access controls to reduce the attack surface and limit the ability of attackers to submit crafted files to vulnerable endpoints. 6. Maintain up-to-date backups and incident response plans to quickly recover from potential service disruptions. 7. Engage with Cisco support or security advisories regularly to stay informed about any further developments or additional patches. 8. Consider deploying additional layered endpoint detection and response (EDR) tools to provide fallback protection during patch rollout.