CVE-2018-0361 in ClamAV
Summary
by MITRE
ClamAV before 0.100.1 lacks a PDF object length check, resulting in an unreasonably long time to parse a relatively small file.
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Analysis
by VulDB Data Team • 04/09/2023
The vulnerability identified as CVE-2018-0361 affects ClamAV versions prior to 0.100.1 and represents a significant performance degradation issue that can be exploited to cause denial of service conditions. This flaw specifically manifests in the PDF parsing component of ClamAV where the software fails to implement proper object length validation during document processing. The absence of these checks allows maliciously crafted PDF files to trigger excessive processing times that can extend to several minutes or even hours for relatively small file sizes, effectively rendering the antivirus system unusable for legitimate scanning operations.
The technical root cause of this vulnerability lies in the improper handling of PDF object structures within ClamAV's parsing engine. When processing PDF documents, the software encounters objects with excessively long length specifications that should normally be rejected or capped at reasonable limits. Without these validation checks, the parser enters into prolonged processing loops attempting to handle what should be invalid or at least highly suspicious object definitions. This behavior creates a resource exhaustion scenario where system CPU and memory resources are consumed disproportionately to the actual file size, leading to significant performance degradation and potential system instability.
This vulnerability directly impacts the operational integrity of security infrastructure by creating a denial of service condition that can be easily triggered through simple malicious PDF files. The attack vector is particularly concerning because it requires minimal sophistication to exploit, making it accessible to attackers with basic knowledge of PDF structure manipulation. The impact extends beyond individual system performance degradation to potentially affect entire network security operations, as ClamAV instances deployed across organizations may become unresponsive during scanning operations, creating security gaps and operational disruptions that can last for extended periods.
The vulnerability aligns with CWE-770, which addresses allocation of resources without limits or with inadequate limits, and demonstrates how insufficient input validation can lead to resource exhaustion attacks. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to Network Denial of Service, and potentially T1566.001 for initial access through malicious email attachments. Organizations utilizing ClamAV for email filtering, file scanning, or endpoint protection are particularly at risk as these systems often process high volumes of files and may not have adequate protection against such time-based denial of service attacks. The vulnerability also reflects poor adherence to secure coding practices that should include input sanitization and resource limitation mechanisms.
The recommended mitigation strategy involves upgrading to ClamAV version 0.100.1 or later, which includes proper PDF object length validation and resource limiting mechanisms. Organizations should also implement additional protective measures such as file size restrictions, content filtering, and monitoring for unusual processing times that may indicate exploitation attempts. Network segmentation and rate limiting of file scanning operations can help reduce the impact of potential exploitation attempts while maintaining overall security posture. Security teams should also consider implementing automated alerting for scanning operations that exceed normal processing time thresholds to quickly identify and respond to potential exploitation attempts.