CVE-2006-4018 in ClamAV
Summary
by MITRE
Heap-based buffer overflow in the pefromupx function in libclamav/upx.c in Clam AntiVirus (ClamAV) 0.81 through 0.88.3 allows remote attackers to execute arbitrary code via a crafted UPX packed file containing sections with large rsize values.
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Analysis
by VulDB Data Team • 06/18/2025
The vulnerability CVE-2006-4018 represents a critical heap-based buffer overflow in Clam AntiVirus version 0.81 through 0.88.3, specifically within the pefromupx function located in libclamav/upx.c. This flaw arises from insufficient input validation when processing UPX packed files, creating a condition where maliciously crafted file structures can trigger memory corruption. The vulnerability manifests when the software encounters sections within UPX packed files that contain excessively large rsize values, which are not properly bounds-checked before memory allocation occurs. This allows attackers to manipulate heap memory layout and potentially execute arbitrary code with the privileges of the ClamAV process. The issue stems from a fundamental failure to validate the size parameters of file sections during decompression operations, creating an exploitable condition that can be leveraged remotely through malicious file delivery.
The technical implementation of this vulnerability involves the manipulation of UPX compression format metadata, specifically targeting the rsize field within section headers. When ClamAV processes a UPX packed file, it attempts to parse section information and allocate heap memory based on the rsize values provided. The pefromupx function fails to validate that these size parameters remain within reasonable bounds, allowing attackers to specify values that exceed the allocated buffer space. This creates a classic heap overflow condition where subsequent memory operations can overwrite adjacent heap chunks or metadata structures. The vulnerability operates under CWE-121, heap-based buffer overflow, and aligns with ATT&CK technique T1059.007 for execution through command and scripting interpreter, as successful exploitation can result in arbitrary code execution. The attack vector requires remote delivery of a specially crafted UPX packed file that, when scanned by ClamAV, triggers the vulnerable code path.
The operational impact of CVE-2006-4018 extends beyond simple code execution to encompass potential system compromise and denial of service conditions. Since ClamAV typically runs with elevated privileges to scan files effectively, successful exploitation could lead to complete system compromise with the privileges of the scanning service. Network administrators and security teams face significant risk when ClamAV is deployed in production environments, as the vulnerability can be exploited through automated scanning of malicious files delivered via email, web downloads, or file sharing systems. The vulnerability affects organizations that rely on ClamAV for malware detection and prevention, potentially creating a backdoor for attackers who can leverage the scanner itself as an attack vector. Additionally, the impact includes potential denial of service scenarios where malformed files cause ClamAV to crash or behave unpredictably, disrupting security operations and potentially masking other malicious activities.
Mitigation strategies for CVE-2006-4018 require immediate action to upgrade to patched versions of ClamAV where the vulnerability has been addressed through proper input validation and bounds checking. Organizations should implement network segmentation and file filtering mechanisms to prevent potentially malicious UPX packed files from reaching systems running vulnerable ClamAV versions. The recommended approach includes deploying updated ClamAV signatures and ensuring all systems are running version 0.88.4 or later, which contains the necessary fixes for this heap overflow condition. Security teams should also consider implementing additional monitoring for unusual ClamAV behavior or crashes that might indicate exploitation attempts. The vulnerability highlights the importance of proper input validation in security software and demonstrates how anti-virus systems themselves can become attack vectors when not properly secured against malformed input. Organizations should conduct thorough vulnerability assessments to identify all systems running affected ClamAV versions and ensure complete remediation through patch management processes. Implementation of additional security controls such as sandboxing for suspicious file analysis and network-based file inspection can provide additional defense in depth against similar vulnerabilities in security tools.