CVE-2005-2919 in ClamAV
Summary
by MITRE
libclamav/fsg.c in Clam AntiVirus (ClamAV) before 0.87 allows remote attackers to cause a denial of service (infinite loop) via a crafted FSG packed executable.
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Analysis
by VulDB Data Team • 07/06/2021
The vulnerability identified as CVE-2005-2919 affects Clam AntiVirus version 0.87 and earlier, specifically within the libclamav/fsg.c component responsible for handling FSG packed executables. This flaw represents a classic denial of service condition that can be exploited remotely by malicious actors to disrupt the normal operation of antivirus systems. The vulnerability resides in the FSG unpacking functionality that is designed to decompress executables packed with the FSG packer, a common tool used by both legitimate software distributors and malware authors for executable compression and obfuscation purposes.
The technical root cause of this vulnerability stems from inadequate input validation and loop termination logic within the FSG unpacking algorithm. When ClamAV encounters a specially crafted FSG packed executable, the unpacking routine enters an infinite loop due to malformed or maliciously constructed FSG headers that cause the decompression algorithm to never reach its expected termination conditions. This occurs because the FSG unpacker does not properly validate the structure of the packed executable headers or implement robust bounds checking mechanisms. The flaw is classified as a CWE-835: Loop with Unreachable Exit Condition, which represents a fundamental programming error where loop termination conditions are either missing or insufficient to prevent infinite execution paths.
From an operational impact perspective, this vulnerability poses significant risks to organizations relying on ClamAV for malware detection and prevention. Remote attackers can exploit this weakness to cause service disruption across multiple systems, potentially leading to complete system unavailability or performance degradation that affects critical network operations. The infinite loop consumes excessive CPU resources and can cause the antivirus daemon to become unresponsive, effectively rendering the system vulnerable to actual malware infections during the period of service disruption. This vulnerability particularly affects environments where ClamAV is used for real-time scanning of network traffic or file transfers, as the denial of service can be triggered through various attack vectors including email attachments, web downloads, or file sharing protocols.
The exploitation of this vulnerability aligns with ATT&CK technique T1499.004, which describes the use of denial of service attacks against services or systems. Organizations using vulnerable versions of ClamAV face potential operational downtime and increased risk of successful malware delivery during the service disruption period. Security practitioners should consider this vulnerability when assessing their endpoint protection strategies, as it demonstrates the importance of proper input validation and robust error handling in security software. The vulnerability also highlights the need for comprehensive testing of unpacking and decompression routines, as these components often represent attack surfaces where malformed input can lead to system instability. Organizations should prioritize immediate patching of affected ClamAV installations to prevent exploitation, as the vulnerability does not require authentication or special privileges to trigger the denial of service condition.