CVE-2008-1835 in ClamAV
Summary
by MITRE
ClamAV before 0.93 allows remote attackers to bypass the scanning enging via a RAR file with an invalid version number, which cannot be parsed by ClamAV but can be extracted by Winrar.
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Analysis
by VulDB Data Team • 07/31/2021
The vulnerability described in CVE-2008-1835 represents a significant security flaw in ClamAV antivirus software versions prior to 0.93, specifically affecting the RAR file handling mechanism within the scanning engine. This issue stems from an inadequate validation process that fails to properly parse RAR file headers, creating a potential bypass mechanism for malicious actors seeking to evade detection. The vulnerability exploits a fundamental weakness in how ClamAV processes archive files, particularly those using the RAR format, which is commonly employed by attackers to deliver malware payloads.
The technical flaw manifests when ClamAV encounters a RAR file containing an invalid version number that cannot be properly parsed by the antivirus engine. While the file can still be successfully extracted by legitimate archive tools such as WinRAR, ClamAV's scanning engine fails to recognize or properly analyze the file contents due to this parsing failure. This discrepancy creates a window of opportunity for attackers to craft malicious RAR files that appear benign to the extraction process but bypass the scanning engine entirely. The vulnerability is classified under CWE-20, representing improper input validation, and demonstrates a classic case of incomplete validation leading to security bypass.
The operational impact of this vulnerability extends beyond simple file detection failures, as it provides attackers with a method to circumvent antivirus protection mechanisms that are critical for endpoint security. When an infected RAR file is processed by ClamAV, the engine's inability to parse the invalid version number results in the file being skipped or improperly analyzed, allowing malicious code to remain undetected within the system. This bypass capability can be particularly dangerous in enterprise environments where ClamAV serves as a primary defense mechanism against malware delivery through compressed archives. The vulnerability affects the core scanning functionality and undermines the trust placed in the antivirus software's ability to identify threats within archive files.
Organizations utilizing ClamAV versions prior to 0.93 face significant risk from this vulnerability, as it can be exploited in targeted attacks where attackers specifically craft RAR files with invalid version numbers to evade detection. The attack vector aligns with techniques described in the MITRE ATT&CK framework under the T1027 category for Obfuscated Files or Information, where attackers manipulate file formats to avoid signature-based detection. Security professionals should implement immediate mitigation measures including upgrading to ClamAV version 0.93 or later, which contains the necessary patches to properly handle RAR file version numbers. Additional protective measures include implementing network-based detection systems that monitor for suspicious RAR file patterns and establishing comprehensive monitoring procedures to identify potential exploitation attempts. The vulnerability underscores the importance of maintaining current antivirus signatures and engine updates to address emerging threats that exploit parsing and validation weaknesses in security software.