CVE-2026-20243 in Secure Endpoint
Summary
by MITRE • 07/01/2026
A vulnerability in the ALZ file format parser of ClamAV could allow an unauthenticated, remote attacker to cause a DoS condition, or possibly other expanded impacts, resulting from memory corruption on an affected device.
This vulnerability is due to improper boundary checks for content in ALZ files during scanning, which may result in an out-of-bounds buffer write. An attacker could exploit this vulnerability by submitting a crafted file that contains ALZ 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 • 07/01/2026
The vulnerability identified in ClamAV's ALZ file format parser represents a critical security flaw that undermines the integrity of antivirus scanning operations. This issue manifests within the parsing logic responsible for processing ALZ compressed files, which are commonly used for archiving and data compression in various computing environments. The ALZ format parser serves as a crucial component within ClamAV's detection framework, where it processes potentially malicious content to identify threats before they can compromise systems. When an attacker successfully exploits this vulnerability, the consequences extend beyond simple denial of service, potentially leading to more severe system instability and operational disruptions.
The technical root cause of this vulnerability stems from inadequate boundary validation mechanisms within the ALZ file parsing code structure. Specifically, the parser fails to properly validate buffer limits when processing compressed content, creating opportunities for out-of-bounds memory writes that can corrupt critical system resources. This type of flaw falls under the CWE-129 category of "Improper Validation of Array Index" and aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, as attackers can manipulate file contents to trigger memory corruption during legitimate scanning operations. The absence of proper input sanitization allows crafted ALZ files to contain maliciously structured data that bypasses normal validation checks, enabling attackers to overwrite adjacent memory locations with arbitrary data.
The operational impact of this vulnerability extends significantly beyond immediate denial of service conditions, potentially creating cascading effects throughout security infrastructure. When ClamAV encounters a malformed ALZ file, the buffer overflow can cause the scanning process to crash or terminate unexpectedly, disrupting ongoing security monitoring activities and potentially leaving systems temporarily unprotected. This disruption is particularly concerning in enterprise environments where ClamAV serves as a primary defense mechanism against malware propagation. The vulnerability also presents indirect risks through potential information disclosure, as memory corruption during parsing operations might expose sensitive data stored in adjacent memory regions. Organizations relying on automated scanning workflows face increased operational overhead when dealing with system restarts and manual intervention requirements.
Mitigation strategies for this vulnerability require immediate attention through software updates and configuration hardening measures. The primary solution involves applying the latest security patches released by ClamAV developers, which typically include enhanced boundary checking mechanisms and improved input validation routines. Network administrators should implement additional monitoring controls to detect anomalous scanning behavior that might indicate exploitation attempts, utilizing intrusion detection systems to identify suspicious file submission patterns. Security teams should also consider implementing file type whitelisting policies that restrict ALZ file processing to trusted sources only, reducing the attack surface available to potential adversaries. In environments where immediate patching is not feasible, temporary workarounds such as disabling ALZ file scanning capabilities or implementing additional content filtering layers can provide interim protection against exploitation attempts.