CVE-2026-20337 in ClamAV
Summary
by MITRE • 08/07/2026
A vulnerability in the zip archive parser of ClamAV could allow an unauthenticated, remote attacker to cause a DoS condition on an affected device.
This vulnerability is due to improper boundary checks for content in zip files during scanning, which may result in an out-of-bounds write condition. An attacker could exploit this vulnerability by submitting a crafted zip file for scanning. A successful exploit could allow the attacker to cause the ClamAV scanning process to terminate, resulting in a DoS condition on the affected software.
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Analysis
by VulDB Data Team • 08/07/2026
This vulnerability resides within the zip archive parsing functionality of ClamAV, a widely deployed open-source antivirus engine that serves as the foundation for numerous security solutions across enterprise and network environments. The flaw manifests as insufficient validation of boundary conditions when processing compressed archive content, creating a potential attack vector that could compromise system availability. ClamAV's extensive deployment in email servers, network appliances, and endpoint protection platforms makes this vulnerability particularly concerning from a threat exploitation perspective.
The technical root cause involves improper input validation during the parsing of zip file structures where the application fails to adequately verify array bounds when processing compressed content. This condition creates an out-of-bounds write scenario that occurs when the parser attempts to write data beyond allocated memory regions within the application's address space. The vulnerability specifically affects the decompression and extraction routines that handle various compression formats within the zip archive, particularly when encountering malformed or crafted archive structures that exceed expected memory boundaries.
From an operational standpoint, this vulnerability presents a significant denial-of-service risk to systems relying on ClamAV for security scanning operations. An unauthenticated remote attacker can trigger the vulnerable condition by simply submitting a maliciously crafted zip file to any system running ClamAV in a scanning capacity. The exploitation results in immediate termination of the ClamAV scanning process, effectively rendering the antivirus functionality unavailable until manual intervention or service restart occurs. This disruption impacts not only the immediate antivirus capabilities but can also affect downstream security operations that depend on successful scanning completion.
The vulnerability aligns with CWE-129, which addresses improper validation of array index bounds, and represents a classic example of memory safety issues that have plagued many software applications over decades. From an adversarial perspective, this vulnerability maps to ATT&CK technique T1499.004, which covers the use of network denial-of-service attacks through application-level exploitation. The impact extends beyond simple service interruption as compromised scanning services can leave systems vulnerable to other attack vectors while security operations are temporarily disabled.
Effective mitigation strategies include applying the latest ClamAV updates that contain patched parsing routines with proper boundary validation, implementing network-level filtering to prevent suspicious zip file transfers, and deploying redundant scanning mechanisms where possible. Organizations should also consider implementing monitoring solutions that can detect service termination events related to antivirus processes as early warning indicators of potential exploitation attempts. Additionally, regular security assessments of deployed ClamAV instances can help identify systems that may be running outdated versions vulnerable to this or similar memory corruption issues.