CVE-2026-20347 in ClamAV
Summary
by MITRE • 08/07/2026
A vulnerability in the Mach-O file format parser of ClamAV could allow an unauthenticated, remote attacker to cause a DoS condition or possibly other expanded impacts as a result of memory corruption on an affected device.
This vulnerability is due to improper boundary checks for content in Mach-O files during scanning, which may result in an out-of-bounds buffer read. An attacker could exploit this vulnerability by submitting a crafted Mach-O file to be scanned by ClamAV on an affected device. 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
The vulnerability under examination represents a critical weakness in ClamAV's Mach-O file format parsing capabilities that exposes systems to remote exploitation without authentication requirements. This issue stems from inadequate validation mechanisms within the antivirus software's file analysis routines, specifically targeting the parser responsible for examining Mach-O binary files used primarily on macOS and iOS operating systems. The flaw manifests as insufficient boundary checking during the parsing process, creating opportunities for memory corruption through malformed input data that exceeds expected buffer limits. Security researchers have identified this vulnerability as particularly dangerous because it affects the core scanning functionality of ClamAV, potentially allowing attackers to disrupt security operations across multiple platforms where the software is deployed.
The technical implementation of this vulnerability operates through a classic out-of-bounds buffer read condition that occurs when ClamAV processes maliciously crafted Mach-O files. During normal operation, the antivirus engine expects specific file structures and data layouts within Mach-O containers, but the absence of proper validation allows attackers to construct files containing oversized or malformed sections that exceed allocated memory boundaries. When the parser attempts to read beyond these predetermined limits, it triggers memory corruption that can manifest in various ways including program termination, stack corruption, or potentially more severe consequences depending on the execution environment. This type of vulnerability falls under the CWE-129 classification for improper validation of array index and is consistent with ATT&CK technique T1566.001 for initial access through spearphishing attachments, as attackers could leverage this weakness to deliver malicious files that disrupt security operations.
The operational impact of this vulnerability extends beyond simple denial-of-service conditions, potentially creating broader security implications for organizations relying on ClamAV for malware detection and prevention. When the scanning process terminates unexpectedly due to buffer overflow conditions, it leaves systems temporarily unprotected against other threats while administrators investigate the issue and restart services. This disruption can be particularly damaging in enterprise environments where continuous security monitoring is essential, as it may create windows of vulnerability during service restoration periods. The attack surface includes any system running ClamAV that processes potentially malicious Mach-O files, whether through email attachments, file transfers, or automated scanning of network resources. Organizations using ClamAV for comprehensive endpoint protection face the risk of having their security infrastructure temporarily compromised, potentially allowing attackers to bypass other protective measures while the scanning service is offline.
Mitigation strategies for this vulnerability should focus on immediate software updates from ClamAV developers, as patches typically address the underlying boundary checking issues through improved input validation and buffer management. Network administrators should implement additional monitoring of ClamAV processes to detect abnormal termination patterns that might indicate exploitation attempts, while also considering the deployment of alternative scanning solutions during patching windows. The implementation of file type restrictions and automated quarantine procedures for Mach-O files can provide additional defense layers, though these measures should complement rather than replace proper software updates. System hardening practices including memory protection mechanisms and process isolation can reduce the potential impact if exploitation occurs, while regular security audits of antivirus configurations help ensure that scanning parameters are properly tuned to prevent similar issues in other components of the security infrastructure. Organizations should also consider implementing network segmentation to limit the potential spread of any compromise that might occur through this vulnerability, ensuring that even if one system is affected, adjacent systems remain protected through proper architectural controls.