CVE-2007-3725 in ClamAV
Summary
by MITRE
The RAR VM (unrarvm.c) in Clam Antivirus (ClamAV) before 0.91 allows user-assisted remote attackers to cause a denial of service (crash) via a crafted RAR archive, resulting in a NULL pointer dereference.
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Analysis
by VulDB Data Team • 01/11/2025
The vulnerability identified as CVE-2007-3725 represents a critical denial of service flaw within ClamAV's RAR archive processing functionality. This issue specifically affects the unrarvm.c component of ClamAV versions prior to 0.91, where a malformed RAR archive can trigger a NULL pointer dereference condition. The vulnerability operates through a user-assisted remote attack vector, meaning that an attacker must convince a victim to open or process a specially crafted RAR file, though the actual exploitation does not require direct user interaction beyond the initial delivery of the malicious archive. The flaw exists in the virtual machine implementation used by ClamAV to handle RAR archives, which is designed to execute potentially malicious code contained within compressed files.
The technical root cause of this vulnerability lies in inadequate input validation and error handling within the RAR decompression engine. When ClamAV processes a crafted RAR archive, the unrarvm.c module fails to properly validate the structure of the archive before attempting to execute its virtual machine instructions. This leads to a situation where the program attempts to dereference a NULL pointer during the processing of malformed archive metadata. The NULL pointer dereference occurs during the virtual machine execution phase, where the program expects certain data structures to be properly initialized but encounters NULL values instead. This type of vulnerability is classified as a CWE-476 NULL Pointer Dereference, which is a common class of software defects that can lead to application crashes and potential exploitation. The vulnerability demonstrates poor defensive programming practices where the code does not adequately check for null return values from allocation or parsing functions before using the returned pointers.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be leveraged to disrupt security operations within environments that rely on ClamAV for malware detection. When a victim processes a maliciously crafted RAR file, the ClamAV daemon or scanning application will crash, potentially causing service interruption for legitimate users and creating opportunities for attackers to exploit the system's temporary unavailability. This is particularly concerning in enterprise environments where ClamAV is used as a primary antivirus solution, as the crash can lead to complete scanning failures and leave systems vulnerable to other threats. The vulnerability affects both manual and automated scanning operations, meaning that even scheduled scans could be disrupted, potentially allowing malware to evade detection during the period when the antivirus service is unavailable. The attack requires minimal sophistication and can be executed through standard file delivery methods, making it a practical concern for security administrators.
Mitigation strategies for this vulnerability should focus on immediate version updates and defensive coding practices. The most effective solution is to upgrade to ClamAV version 0.91 or later, where the NULL pointer dereference has been addressed through improved input validation and error handling. System administrators should also implement additional defensive measures such as restricting access to potentially malicious archives through network filtering, implementing sandboxed environments for archive processing, and monitoring for unusual crash patterns in antivirus services. The vulnerability highlights the importance of proper memory management and input validation in security software, where the processing of untrusted data should always include robust error checking. Organizations should also consider implementing multiple layers of defense, including network-based malware detection, endpoint protection, and regular security audits of their antivirus configurations to prevent similar issues from occurring in other components of their security infrastructure. This vulnerability serves as a reminder of the critical importance of thorough input validation in security tools, as the failure to properly handle malformed input can result in complete service disruption.