CVE-2026-20339 in ClamAV
Summary
by MITRE • 08/07/2026
A vulnerability in the PESpin 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 PESpin files during scanning, which may result in an integer overflow. An attacker could exploit this vulnerability by submitting a crafted file that contains PESpin 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 identified in ClamAV's PESpin file format parser represents a critical security weakness that undermines the integrity of antivirus scanning operations. This flaw exists within the parsing mechanism responsible for processing PESpin formatted files, which are commonly used in malware analysis and detection workflows. The issue manifests as insufficient validation of file boundaries during the scanning process, creating opportunities for malicious actors to manipulate the parser's behavior through carefully crafted input files. Such vulnerabilities are particularly dangerous in security software environments where the integrity of scanning processes directly impacts system protection capabilities.
Technical exploitation of this vulnerability relies on the absence of proper boundary checks within the PESpin parser implementation, leading to potential integer overflow conditions during memory allocation operations. When ClamAV encounters a malformed PESpin file containing maliciously constructed data structures, the parser fails to validate input parameters properly, resulting in arithmetic overflow that corrupts memory regions allocated for processing. This type of vulnerability falls under the CWE-190 category of Integer Overflow or Wraparound, which is classified as a common weakness in software security implementations. The integer overflow occurs when the parser attempts to calculate memory requirements based on corrupted input values, causing the system to allocate insufficient memory or attempt operations beyond valid memory boundaries.
The operational impact of this vulnerability extends beyond simple denial-of-service conditions, potentially enabling more sophisticated attack vectors that could compromise the overall security posture of systems relying on ClamAV for protection. When the scanning process terminates unexpectedly due to memory corruption, it creates gaps in malware detection coverage that attackers can exploit to bypass security controls. The DoS condition affects not only individual file scanning operations but can also impact entire scanning workflows, potentially causing cascading failures in security infrastructure. This vulnerability demonstrates how seemingly minor parsing flaws can create significant operational risks in security software environments where reliability and continuous operation are paramount for effective threat detection.
Mitigation strategies for this vulnerability should focus on immediate patching of affected ClamAV versions while implementing additional defensive measures to prevent exploitation attempts. Organizations should prioritize updating their ClamAV installations to versions containing fixes for the PESpin parsing logic, ensuring that boundary checks are properly implemented to prevent integer overflow conditions. Network security controls should include monitoring for suspicious file upload patterns and implementing sandboxing mechanisms for unknown file types before scanning. The ATT&CK framework's T1078 technique of Valid Accounts and T1566 technique of Phishing with Malicious Attachments could be relevant in understanding how attackers might exploit this vulnerability through crafted email attachments or web downloads, making it essential to implement layered defenses that detect and prevent such attack vectors from reaching vulnerable systems.