CVE-2006-4626 in Avast! Antivirus
Summary
by MITRE
Heap-based buffer overflow in alwil avast! Anti-virus Engine before 4.7.869 allows remote attackers to execute arbitrary code via a crafted LHA file that contains extended headers with file and directory names whose concatenation triggers the overflow.
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Analysis
by VulDB Data Team • 06/16/2025
The vulnerability described in CVE-2006-4626 represents a critical heap-based buffer overflow within the alwil avast! Anti-virus Engine version 4.7.869 and earlier. This flaw exists in the file processing logic that handles LHA (LHArc) archive files, specifically when these archives contain extended headers with file and directory names that, when concatenated, exceed the allocated buffer space. The vulnerability stems from inadequate input validation and memory management within the anti-virus engine's decompression and parsing routines. Attackers can exploit this weakness by crafting malicious LHA files with specially constructed extended headers that force the engine to write beyond the bounds of allocated heap memory, potentially leading to arbitrary code execution.
The technical implementation of this vulnerability involves the anti-virus engine's handling of extended header information within LHA archives. When processing these archives, the engine allocates a fixed-size buffer to store concatenated file and directory names from extended headers. However, the engine fails to properly validate the length of these concatenated strings before copying them into the allocated buffer space. This oversight creates a classic heap-based buffer overflow condition where attacker-controlled data can overwrite adjacent heap memory locations, potentially corrupting pointers, return addresses, or other critical program state information. The vulnerability specifically affects the parsing of LHA files that contain extended headers, making it particularly relevant for anti-virus engines that process compressed archives as part of their threat detection mechanisms.
From an operational impact perspective, this vulnerability presents a significant risk to systems running vulnerable versions of the avast! anti-virus engine. Attackers can remotely execute arbitrary code on systems by delivering malicious LHA files through various attack vectors including email attachments, web downloads, or compromised file sharing networks. The exploitability of this vulnerability is enhanced by the fact that anti-virus engines typically run with elevated privileges to perform their scanning functions, potentially allowing attackers to achieve system compromise. This vulnerability directly impacts the security posture of organizations relying on the affected anti-virus engine, as it creates a potential attack surface where legitimate anti-virus functionality becomes a vector for malicious code execution. The risk is particularly elevated in environments where users frequently interact with potentially malicious file attachments or where automated scanning processes encounter untrusted archive files.
The mitigation strategy for CVE-2006-4626 centers on upgrading to avast! Anti-virus Engine version 4.7.869 or later, which contains the necessary patches to address the buffer overflow condition. Organizations should prioritize updating their anti-virus software to prevent exploitation of this vulnerability. Additionally, system administrators should implement network-level controls to restrict access to potentially malicious LHA files and employ sandboxing techniques for suspicious archive file processing. Security monitoring should include detection of unusual anti-virus engine behavior or memory access patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-121 heap-based buffer overflow classification and represents a technique that could be mapped to ATT&CK tactics such as execution and privilege escalation, as it allows for arbitrary code execution with the privileges of the anti-virus process. Organizations should also consider implementing multi-layered security controls including email filtering, web proxy filtering, and endpoint protection to reduce the risk of encountering malicious LHA files in the first place.