CVE-2007-2029 in ClamAV
Summary
by MITRE
File descriptor leak in the PDF handler in Clam AntiVirus (ClamAV) allows remote attackers to cause a denial of service via a crafted PDF file.
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Analysis
by VulDB Data Team • 07/14/2021
The vulnerability identified as CVE-2007-2029 represents a critical file descriptor leak within the PDF handling component of Clam AntiVirus, a widely deployed open-source antivirus solution. This flaw exists in the manner in which ClamAV processes malformed PDF documents, specifically within its PDF handler module that is responsible for parsing and analyzing PDF files for potential threats. The vulnerability manifests when ClamAV encounters a specially crafted PDF file that triggers improper resource management during the parsing process, leading to the accumulation of unreleased file descriptors in the system's resource table.
The technical nature of this vulnerability aligns with CWE-404, which describes improper resource release or reclaim, specifically focusing on the failure to properly close file descriptors. When ClamAV processes the malicious PDF file, the PDF handler fails to properly clean up file descriptor resources that were allocated during the parsing operation. This resource leak occurs repeatedly each time the vulnerable code path is executed, causing the system to gradually consume available file descriptors until the process reaches its maximum limit. The underlying mechanism involves the PDF parser's inability to handle certain malformed PDF structures properly, resulting in execution paths that bypass normal cleanup routines and leave file handles open indefinitely.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it creates a reliable denial of service condition that can be exploited by remote attackers without requiring authentication or elevated privileges. An attacker can simply craft a malicious PDF file and deliver it through any means that would cause ClamAV to process the file, such as email attachments, web downloads, or file sharing systems. Once processed, the continuous accumulation of leaked file descriptors causes ClamAV to eventually become unresponsive, as the system cannot allocate new file descriptors for legitimate operations. This creates a cascading effect where the antivirus system becomes ineffective, potentially leaving the system vulnerable to actual malware while appearing to be operational, thus undermining the security posture of environments relying on ClamAV for protection.
Mitigation strategies for this vulnerability should focus on both immediate remediation and long-term architectural improvements. The most direct solution involves applying the vendor-provided patch that corrects the PDF handler's resource management logic to ensure proper cleanup of file descriptors regardless of the PDF file's structure. Organizations should also implement monitoring systems to track file descriptor usage patterns in ClamAV processes, enabling early detection of resource exhaustion conditions. Additionally, implementing input validation and sandboxing techniques for PDF processing can provide defense-in-depth measures that reduce the likelihood of exploitation. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service and the T1070.004 technique involving file and directory permissions modification, as the exploitation directly impacts system availability through resource consumption. Organizations should also consider implementing network segmentation and content filtering to prevent the delivery of potentially malicious PDF files to systems running ClamAV, reducing the attack surface and limiting the potential impact of such vulnerabilities.