CVE-2023-20197 in ClamAV
Summary
by MITRE • 08/17/2023
A vulnerability in the filesystem image parser for Hierarchical File System Plus (HFS+) of ClamAV could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to an incorrect check for completion when a file is decompressed, which may result in a loop condition that could cause the affected software to stop responding. An attacker could exploit this vulnerability by submitting a crafted HFS+ filesystem image to be scanned by ClamAV on an affected device. A successful exploit could allow the attacker to cause the ClamAV scanning process to stop responding, resulting in a DoS condition on the affected software and consuming available system resources. For a description of this vulnerability, see the ClamAV blog .
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 02/04/2025
The vulnerability identified as CVE-2023-20197 represents a critical denial of service weakness within ClamAV's handling of Hierarchical File System Plus (HFS+) filesystem images. This flaw specifically manifests in the decompression validation logic where the software fails to properly verify completion status during file extraction processes. The improper validation creates a condition where the decompression routine can enter an infinite loop, causing the scanning process to become unresponsive and consume excessive system resources. This vulnerability impacts ClamAV deployments across various operating systems including Windows, macOS, and Linux platforms where HFS+ filesystems are processed. The issue stems from insufficient bounds checking and loop termination conditions within the HFS+ parser implementation, creating a scenario where malformed or crafted filesystem images can trigger the problematic code path. The vulnerability affects ClamAV versions prior to 1.4.0, making it particularly concerning for organizations relying on older software versions for their antivirus protection.
The technical exploitation of this vulnerability requires an attacker to craft a malicious HFS+ filesystem image that triggers the specific decompression loop condition. When ClamAV processes this crafted image during routine scanning operations, the software enters a state where it continuously loops through decompression routines without proper termination. This behavior results in the scanning process consuming all available CPU cycles and memory resources, effectively rendering the antivirus software incapable of performing its intended function. The vulnerability operates at the application layer and requires no authentication or specialized privileges to exploit, making it particularly dangerous in environments where ClamAV is used for automated scanning of untrusted content. The attack vector is straightforward since the vulnerability is triggered during normal file processing when ClamAV encounters HFS+ formatted images. This type of vulnerability aligns with CWE-835, which addresses infinite loops or iterations without proper termination conditions, and demonstrates how improper loop control can lead to resource exhaustion and denial of service conditions.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire security infrastructures. Organizations relying on ClamAV for endpoint protection or network scanning may experience complete system unavailability when the scanning process becomes unresponsive due to the infinite loop condition. This can result in delayed threat detection, increased system maintenance overhead, and potential security gaps during the time when ClamAV is non-operational. The resource consumption pattern typical of such vulnerabilities makes detection challenging since the system may appear to be functioning normally while the scanning process is consuming resources without progress. In high-volume scanning environments, the vulnerability could be exploited to create cascading failures across multiple systems, particularly when ClamAV is integrated into larger security orchestration frameworks. The vulnerability also represents a potential attack surface for adversaries seeking to disrupt security operations, as it can be triggered through legitimate scanning workflows without requiring privileged access. This aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how application-level flaws can be leveraged to achieve system-level disruption.
Organizations should immediately implement mitigations including updating to ClamAV version 1.4.0 or later where the vulnerability has been patched. The patch addresses the decompression validation logic by implementing proper loop termination conditions and bounds checking to prevent infinite iteration scenarios. Administrators should also consider implementing additional scanning controls such as limiting the file types processed or implementing timeout mechanisms for scanning operations. Network segmentation and monitoring should be enhanced to detect unusual resource consumption patterns that may indicate exploitation attempts. Regular vulnerability assessments should include verification of ClamAV configurations and monitoring for potential malicious HFS+ image submissions. The vulnerability highlights the importance of proper input validation and loop control in security software, particularly when handling potentially malicious file formats. Organizations should also implement automated patch management processes to ensure timely deployment of security updates. Additional defensive measures include deploying multiple antivirus solutions to provide redundancy and implementing file type filtering to reduce exposure to vulnerable file formats. The incident underscores the necessity of thorough testing of security software against malformed inputs and the importance of maintaining current security tool versions to protect against known vulnerabilities.