CVE-2026-20338 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 memory handling when processing content in zip files during scanning. 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 as a result of a memory double-free, resulting in a DoS condition on the affected software.
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Analysis
by VulDB Data Team • 08/07/2026
The vulnerability under discussion represents a critical denial-of-service weakness within ClamAV's zip archive parsing functionality that exposes systems to remote exploitation without authentication requirements. This flaw resides in the memory management mechanisms responsible for processing compressed content during antivirus scanning operations, creating an avenue for malicious actors to disrupt service availability through carefully constructed malicious archives.
The technical root cause of this vulnerability stems from improper memory handling practices within ClamAV's zip file parser implementation. When processing specially crafted zip archives, the software encounters a scenario that triggers a memory double-free condition during the decompression and scanning phases. This occurs when the application attempts to release the same memory block twice, leading to undefined behavior and ultimately causing the scanning process to crash or terminate unexpectedly. The vulnerability is classified as a memory corruption issue that directly impacts the application's stability and operational continuity.
From an operational perspective, this vulnerability presents significant risk to organizations relying on ClamAV for network security monitoring and endpoint protection. The remote nature of the exploit means that attackers can initiate DoS conditions from external networks without requiring any authentication credentials or privileged access. This makes the vulnerability particularly dangerous as it allows for widespread disruption across multiple systems that utilize ClamAV scanning services, potentially affecting email servers, file servers, and network security appliances that depend on the software for threat detection.
The impact of this vulnerability extends beyond simple service disruption to encompass potential business continuity issues and increased administrative overhead. Organizations may experience temporary loss of scanning capabilities during exploitation attempts, requiring system administrators to restart services and potentially reconfigure security policies. The vulnerability also creates opportunities for attackers to conduct reconnaissance activities by testing multiple malicious archives to identify the most effective attack vectors.
Security professionals should consider this vulnerability in the context of broader software reliability frameworks and memory safety standards. The flaw aligns with common weakness enumerations such as CWE-415, which addresses double free conditions in memory management, and demonstrates the importance of proper resource handling in security applications. From an adversarial perspective, this vulnerability maps to ATT&CK technique T1499.004, which involves network disruption through service denial, making it a valuable target for threat actors seeking to disrupt organizational operations.
Mitigation strategies should focus on immediate patch application from ClamAV vendors to address the memory handling issues within the zip parser module. Organizations should also implement network segmentation and access controls to limit exposure of vulnerable ClamAV instances to untrusted networks. Additionally, deploying monitoring solutions that can detect unusual scanning process behavior or resource consumption patterns may help identify exploitation attempts before they result in complete service disruption. Regular vulnerability assessments and security audits should be conducted to identify similar memory management issues in other security software components.
The vulnerability highlights the critical importance of robust memory management practices in security applications where reliability directly impacts organizational security posture. Given that antivirus scanning is often a core component of enterprise security infrastructure, addressing such flaws promptly becomes essential for maintaining overall defensive capabilities. Organizations should also consider implementing redundant scanning mechanisms or alternative security solutions to ensure continued protection even during patch deployment windows.