CiscoClamAV Vulnerabilities Let Remote Attackers Crash Antivirus Scanning With Crafted Files

Cisco has disclosed seven high-severity vulnerabilities in ClamAV that could allow unauthenticated remote attackers to disrupt antivirus scanning by submitting specially crafted files.

These vulnerabilities are tracked as CVE-2026-20337, CVE-2026-20338, CVE-2026-20339, CVE-2026-20345, CVE-2026-20346, CVE-2026-20347, and CVE-2026-20348, and have been assigned a maximum CVSS score of 7.5.

ClamAV Vulnerabilities

The issues are detailed in the Cisco advisory titled “cisco-sa-clamav-WuuvVd26,” published on August 7 and updated on August 10. Cisco stated that successful exploitation of these vulnerabilities can interrupt the ClamAV scanning process, leading to a denial-of-service condition.

Importantly, these vulnerabilities are independent of each other, allowing an attacker to trigger each issue separately if the affected parser is accessible during a scanning workflow.

All seven vulnerabilities stem from unsafe parsing of attacker-controlled content. CVE-2026-20337 involves an out-of-bounds write in ZIP archive processing due to inadequate boundary checks.

CVE-2026-20338 relates to a double-free error in the ZIP parser caused by improper memory handling. Both vulnerabilities can be triggered with malicious ZIP files, and proof-of-concept exploit code is publicly available for them.

CVE-2026-20339 affects the PESpin parser, where insufficient boundary validation can lead to integer overflow and subsequent memory corruption. CVE-2026-20345 is caused by faulty endian conversion during GPT parsing, leading to an out-of-bounds buffer write.

CVE-2026-20346 and CVE-2026-20347 are both out-of-bounds read flaws occurring in PDF and Mach-O parsing, respectively. Lastly, CVE-2026-20348 impacts XAR processing and can cause memory corruption when scanning a crafted XAR-containing file.

Cisco noted that several of these vulnerabilities may have “other expanded impacts” due to memory corruption. However, the advisory confirms that denial of service is the primary outcome.

• CVE-2026-20337 – ClamAV ZIP parser out-of-bounds write vulnerability; a crafted ZIP file can crash the scanning process and cause denial of service. CVSS: 7.5 (High)
• CVE-2026-20338 – ClamAV ZIP parser double-free memory corruption vulnerability; malicious ZIP content can terminate scanning operations. CVSS: 7.5 (High)
• CVE-2026-20339 – ClamAV PESpin parser integer-overflow vulnerability; crafted PESpin files can trigger memory corruption and denial of service. CVSS: 7.5 (High)
• CVE-2026-20345 – ClamAV GPT parser out-of-bounds buffer write vulnerability caused by improper endian conversion; crafted GPT files can disrupt scanning. CVSS: 7.5 (High)
• CVE-2026-20346 – ClamAV PDF parser out-of-bounds buffer read vulnerability; malicious PDFs can cause memory corruption and crash the scanner. CVSS: 7.5 (High)
• CVE-2026-20347 – ClamAV Mach-O parser out-of-bounds buffer read vulnerability; crafted Mach-O files can terminate antivirus scanning. CVSS: 7.5 (High)
• CVE-2026-20348 – ClamAV XAR parser memory-corruption vulnerability; malicious XAR-containing files can crash the scanning engine and cause denial of service. CVSS: 7.5 (High)

The vendor also stated that it is not aware of any malicious exploitation at this time. Public proof-of-concept exploits are available only for CVE-2026-20337 and CVE-2026-20338.

These vulnerabilities affect Cisco Secure Endpoint Connector installations on Windows, Linux, and macOS. Windows deployments have been given a High Cisco Security Impact Rating because the ClamAV scanning process operates in a privileged security context.

In contrast, Linux and macOS have been rated Medium as their scanning runs with lower privileges. While Cisco Secure Endpoint Private Cloud is not directly vulnerable, the endpoint connectors it distributes are affected.

No workaround is currently available. Cisco is preparing updated Secure Endpoint Connector releases for all three operating systems, with release numbers yet to be determined and an anticipated August 2026 release. Private Cloud version 4.2.8 and later will support distributing the updated endpoint software once it is released.

Security teams should identify any exposed connector versions and prioritize updates for Windows endpoints. They should deploy the updated connectors via the Secure Endpoint portal or normal Private Cloud content-update processes as soon as they become available.

Until patches are installed, organizations should treat untrusted archives, PDFs, disk images, and executable files submitted for scanning as potential availability risks, especially in email gateways, file-upload services, and automated malware-analysis pipelines.

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