CVE-2007-4787 in Sophos
Summary
by MITRE
The virus detection engine in Sophos Anti-Virus before 2.49.0 does not properly process malformed (1) CAB, (2) LZH, and (3) RAR files with modified headers, which might allow remote attackers to bypass malware detection.
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Analysis
by VulDB Data Team • 03/15/2021
The vulnerability described in CVE-2007-4787 represents a critical flaw in the virus detection engine of Sophos Anti-Virus software versions prior to 2.49.0. This issue stems from insufficient validation mechanisms within the software's decompression and file processing routines, specifically affecting three common archive formats that are frequently used in malware distribution campaigns. The flaw allows attackers to craft specially modified archive files with altered headers that can evade detection by the antivirus engine, potentially enabling the execution of malicious code without being flagged by the security system.
The technical implementation of this vulnerability involves the improper handling of archive file headers during the decompression process. When Sophos Anti-Virus encounters CAB, LZH, or RAR files with modified headers, the detection engine fails to properly validate the file structure and content integrity checks. This processing failure occurs at the core level of the antivirus engine where file metadata and header information should be rigorously examined before content analysis begins. The vulnerability manifests because the software's parsing logic does not adequately distinguish between legitimate and malicious modifications to archive file structures, allowing attackers to manipulate header information in ways that bypass signature-based and heuristic detection mechanisms.
From an operational perspective, this vulnerability creates a significant security risk for organizations relying on Sophos Anti-Virus for endpoint protection. Attackers can exploit this flaw by creating archive files with modified headers that contain malicious payloads, knowing that these files will likely be accepted by the antivirus system without proper alerting or blocking. The impact extends beyond simple malware evasion to potentially enable more sophisticated attack vectors, as these modified archives can be used to deliver various types of malicious software including trojans, rootkits, and other persistent threats that might otherwise be detected and neutralized by proper antivirus functionality. The vulnerability particularly affects environments where users frequently download and execute files from untrusted sources, as these modified archive files can easily bypass the security controls in place.
The technical characteristics of this vulnerability align with CWE-129, which addresses improper validation of input boundaries, and can be mapped to ATT&CK technique T1059.007 for execution through scripts and T1027 for obfuscated files and information. Organizations should implement immediate mitigation strategies including updating to Sophos Anti-Virus version 2.49.0 or later, which contains the necessary fixes for proper header validation and file structure checking. Additionally, security teams should consider implementing additional layers of protection such as network-based intrusion detection systems, application whitelisting policies, and enhanced monitoring of file execution patterns to detect potential exploitation attempts. The vulnerability also underscores the importance of regular security updates and the need for comprehensive testing of antivirus solutions to ensure they properly handle edge cases and malformed inputs that attackers might leverage for evasion purposes.