CVE-2026-20346 in ClamAV
Summary
by MITRE • 08/07/2026
A vulnerability in the PDF 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 PDF files during scanning, which may result in an out-of-bounds buffer read. An attacker could exploit this vulnerability by submitting a crafted PDF 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 discussion represents a critical flaw in ClamAV's PDF parsing functionality that exposes systems to remote exploitation without authentication requirements. This security weakness stems from inadequate input validation mechanisms within the antivirus software's file format analysis capabilities, specifically targeting the PDF file parser component. The flaw manifests when ClamAV processes maliciously crafted PDF documents, creating a dangerous condition where the application fails to properly validate buffer boundaries during content parsing operations.
The technical root cause of this vulnerability can be categorized as a buffer overflow condition, more precisely classified as an out-of-bounds read operation that falls under CWE-125. This occurs when the PDF parser attempts to access memory locations beyond the allocated buffer boundaries, leading to unpredictable behavior and potential system instability. The vulnerability exists in the parsing logic where ClamAV does not adequately verify the size constraints of PDF elements before attempting to process them, creating an opportunity for attackers to craft malformed PDF files that trigger memory corruption.
From an operational impact perspective, this vulnerability presents a significant threat to organizations relying on ClamAV for malware detection and prevention. The DoS condition resulting from exploitation can disrupt critical security operations by terminating the scanning process entirely, leaving systems vulnerable to other threats while the antivirus service remains non-functional. This creates a cascading effect where legitimate security monitoring capabilities are temporarily disabled, potentially allowing malicious payloads to bypass detection mechanisms. The vulnerability's remote exploitability means that attackers can trigger the condition without requiring physical access or authentication credentials.
The attack vector for this vulnerability involves sending a specially crafted PDF file to any system running ClamAV in a scanning configuration. This could occur through email attachments, web downloads, or file transfers, making it particularly dangerous in enterprise environments where automated scanning processes are common. The low barrier to exploitation means that even non-technical attackers can potentially trigger the DoS condition, while more sophisticated adversaries might attempt to leverage the memory corruption for additional attack vectors.
Security professionals should prioritize immediate mitigation of this vulnerability through software updates from ClamAV maintainers, as the flaw represents a significant risk to system availability and security operations. Organizations should also consider implementing additional network segmentation and monitoring to detect potential exploitation attempts, while maintaining backup scanning mechanisms to ensure continuous protection. The vulnerability's classification under ATT&CK technique T1566 - "Phishing" and T1498 - "Network Denial of Service" highlights the multi-faceted nature of the threat, requiring comprehensive defensive strategies across multiple security domains.