CVE-2026-20348 in ClamAV
Summary
by MITRE • 08/07/2026
A vulnerability in the XAR 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 XAR files during scanning. An attacker could exploit this vulnerability by submitting a crafted file that contains XAR content 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 in ClamAV's XAR file format parser represents a critical security weakness that exposes systems to remote denial of service attacks and potential memory corruption scenarios. This issue affects the antivirus software's ability to properly handle XAR (XML Archive) files, which are commonly used for packaging and distributing software components. The flaw manifests when ClamAV attempts to parse XAR content during routine scanning operations, creating a pathway for malicious actors to disrupt normal system operations.
The technical root cause of this vulnerability lies in inadequate boundary checking mechanisms within the XAR parser implementation. When processing malformed or specially crafted XAR files, the parser fails to validate input limits and memory allocation boundaries, leading to potential buffer overflows or memory corruption conditions. This weakness aligns with CWE-129, which addresses insufficient validation of length of inputs, and CWE-787, concerning out-of-bounds write operations. The improper handling of XAR file structures allows attackers to manipulate memory layout during parsing, potentially causing the scanning process to crash or behave unpredictably.
From an operational perspective, this vulnerability creates significant risk for organizations relying on ClamAV for endpoint protection. Remote attackers can exploit this weakness without requiring authentication credentials, making it particularly dangerous in environments where automated scanning occurs across multiple systems. The DoS condition impacts not only individual devices but can also affect broader network security operations, as infected systems may become unavailable for critical security functions. Additionally, the potential for memory corruption suggests that sophisticated exploitation could lead to more severe consequences beyond simple service disruption.
The attack vector is straightforward yet effective, requiring only that an attacker successfully deliver a malicious XAR file to a target system where ClamAV is actively scanning. This could occur through various channels including email attachments, web downloads, or file sharing protocols, making the vulnerability accessible across multiple threat surfaces. The impact extends beyond immediate service disruption as it undermines the reliability of the antivirus solution itself, potentially leaving systems more vulnerable to other attacks during the period when the scanning process is compromised.
Organizations should implement immediate mitigations including updating to patched versions of ClamAV where available, implementing network-level restrictions on XAR file processing, and monitoring for suspicious scanning activities. The vulnerability demonstrates the importance of proper input validation in security software and highlights the need for comprehensive testing of file format parsers. Security teams should also consider implementing alternative scanning strategies for XAR content and establishing incident response procedures to address potential exploitation attempts. This weakness serves as a reminder that even security tools themselves can contain vulnerabilities that attackers may leverage to compromise system availability and integrity, emphasizing the critical nature of maintaining up-to-date security solutions and conducting regular vulnerability assessments across all security infrastructure components.