CVE-2005-1923 in ClamAV
Summary
by MITRE
The ENSURE_BITS macro in mszipd.c for Clam AntiVirus (ClamAV) 0.83, and other versions vefore 0.86, allows remote attackers to cause a denial of service (CPU consumption by infinite loop) via a cabinet (CAB) file with the cffile_FolderOffset field set to 0xff, which causes a zero-length read.
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Analysis
by VulDB Data Team • 07/05/2021
The CVE-2005-1923 vulnerability represents a critical denial of service flaw in Clam AntiVirus versions prior to 0.86, specifically within the mszipd.c component that handles cabinet file processing. This vulnerability exploits a fundamental flaw in the ENSURE_BITS macro implementation, which is responsible for bit manipulation operations during decompression of compressed files. The issue manifests when processing cabinet files with malformed cffile_FolderOffset fields set to 0xff, creating a condition that leads to infinite loop execution and subsequent CPU exhaustion. The vulnerability demonstrates a classic case of insufficient input validation and improper error handling in archive decompression routines, where the software fails to properly validate the offset values before attempting to process them.
The technical exploitation of this vulnerability occurs through a carefully crafted cabinet file that contains a cffile_FolderOffset field explicitly set to 0xff, which in binary terms represents a value that triggers the macro to attempt a zero-length read operation. This specific value creates a scenario where the decompression logic enters an infinite loop, continuously processing the same invalid offset without proper termination conditions. The ENSURE_BITS macro, designed to ensure sufficient bits are available for processing, becomes trapped in a state where it repeatedly attempts to read zero-length data segments, consuming excessive CPU resources and effectively rendering the system unavailable to process legitimate files. This behavior aligns with CWE-835, which describes the weakness of infinite loops or iterations without proper termination conditions, and represents a direct violation of proper input validation principles.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it creates a significant threat to system availability and service integrity within environments relying on ClamAV for malware detection. When exploited, the infinite loop consumes 100% of available CPU cycles, preventing the antivirus engine from processing other files or performing its core scanning functions. This denial of service condition affects not only individual systems but can also impact entire network infrastructures where ClamAV is deployed as a centralized security solution. The vulnerability particularly affects environments using older ClamAV versions in production, as the software architecture did not include proper bounds checking or loop termination mechanisms to handle malformed input data. Organizations utilizing ClamAV for email filtering, file scanning, or endpoint protection would experience complete service disruption during exploitation, potentially leading to security gaps while the system remains unresponsive to legitimate threat detection requests.
Mitigation strategies for CVE-2005-1923 require immediate deployment of ClamAV version 0.86 or later, which includes proper input validation and bounds checking for cabinet file processing. System administrators should implement comprehensive patch management procedures to ensure all ClamAV installations are updated to versions containing the fix, which typically involves modifications to the ENSURE_BITS macro to properly validate offset values before processing. Additional defensive measures include implementing file type filtering at network boundaries to prevent suspicious cabinet files from reaching ClamAV scanning engines, deploying intrusion detection systems that can identify anomalous CPU usage patterns, and establishing monitoring protocols to detect and alert on excessive resource consumption by antivirus processes. The vulnerability also highlights the importance of implementing proper software security testing including fuzzing and boundary condition testing to identify similar issues in decompression and parsing routines. From an ATT&CK framework perspective, this vulnerability maps to techniques involving resource exhaustion and denial of service, specifically targeting the execution of security software to compromise system availability and potentially create windows of opportunity for other attacks.