Critical ClamAV Vulnerabilities Let Attackers Trigger DoS

Key Takeaways

• Cisco’s ClamAV antivirus engine contains multiple high-severity vulnerabilities.
• These flaws enable remote attackers to trigger a denial-of-service (DoS) condition by crashing the scanning process.
• Affected platforms include Cisco Secure Endpoint Connector deployments on Windows, Linux, and macOS.
• The highest impact is on Windows (CVSS 7.5), where the system may become unresponsive.
• Patches are available, and upgrading to fixed versions is the only effective mitigation.

Critical ClamAV Vulnerabilities Expose Cisco Endpoints to DoS Attacks

Multiple critical vulnerabilities have been discovered within Cisco’s ClamAV antivirus engine, posing a significant risk of denial-of-service (DoS) attacks. These flaws allow unauthenticated remote attackers to crash the antivirus scanning process, directly impacting the stability and functionality of affected Cisco Secure Endpoint Connector deployments across various operating systems.

Vulnerability Details and Impact

The vulnerabilities, stemming from improper memory handling, boundary checks, and resource management, are present in several ClamAV file format parsers, including PE, FSG, 7z, InstallShield, PESpin, ALZ, and DMG. Attackers can exploit these weaknesses by crafting malicious files in these formats and delivering them to an endpoint. Upon scanning, the malformed files can trigger conditions such as out-of-bounds writes, memory overreads, and integer overflows on 32-bit platforms, leading to the termination of the ClamAV process and temporary consumption of system resources, thereby causing a DoS.

Cisco officially addressed these issues in Cisco Security Advisory cisco-sa-clamav-88cFYyxR, released on July 1, 2026. The advisory highlights that while Cisco Secure Endpoint Private Cloud itself is not directly vulnerable, the connectors it distributes inherit these ClamAV flaws and require immediate updates.

Platform-Specific Severity

The impact of these vulnerabilities varies depending on the operating system:

• Windows: Rated High (CVSS 7.5). On Windows, the ClamAV scanning process often operates with elevated privileges. A crash in this context can directly destabilize the endpoint, potentially rendering it unresponsive and necessitating manual intervention, such as a system reboot.
• Linux and macOS: Rated Medium. While exploitation will still terminate the scanning engine, delaying or blocking malware detection, ClamAV typically runs with reduced privileges on these platforms. Consequently, a DoS primarily disrupts scanning operations rather than causing widespread system instability.

Cisco emphasizes that previous ClamAV parsing vulnerabilities have consistently led to disruptions in scanning and, in some instances, complete scan failures. Historically, in environments with weaker process privileges and platform protections, similar flaws have even facilitated remote code execution, underscoring the inherent risks associated with security engines that routinely process untrusted input.

What You Should Do

• Immediate Patching: Cisco reports that no practical workarounds exist for these ClamAV vulnerabilities. The only effective mitigation is to upgrade to the documented fixed versions of the Secure Endpoint Connector for Windows, Linux, and Mac.
• Utilize Cisco Secure Endpoint Portal: Updated Secure Endpoint Connector releases are available through the Cisco Secure Endpoint portal. Affected customers should prioritize these upgrades as part of their regular content and software update cycles.
• Review Documentation: Security teams should consult the associated Cisco bug IDs and CVE entries for precise build numbers, deployment instructions, and any specific guidance relevant to their environment.
• Resource Planning: Before initiating upgrades, ensure that endpoints have adequate system resources to prevent any potential issues during the update process.

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