CVE-2013-2021 in ClamAV
Summary
by MITRE
pdf.c in ClamAV 0.97.1 through 0.97.7 allows remote attackers to cause a denial of service (out-of-bounds-read) via a crafted length value in an encrypted PDF file.
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Analysis
by VulDB Data Team • 05/10/2021
The vulnerability identified as CVE-2013-2021 represents a critical out-of-bounds read flaw within ClamAV's PDF processing module, specifically affecting versions 0.97.1 through 0.97.7. This issue manifests in the pdf.c component which handles the parsing and analysis of pdf files for malware detection. The vulnerability arises from insufficient input validation when processing encrypted pdf documents, where a maliciously crafted length value within the pdf structure can trigger unexpected memory access patterns. The flaw enables remote attackers to exploit this weakness by crafting specially designed pdf files that, when processed by the vulnerable ClamAV version, cause the application to read memory locations beyond the intended buffer boundaries. This out-of-bounds memory access typically results in application crashes or denial of service conditions, effectively rendering the antivirus scanning functionality unavailable to users. The technical implementation of this vulnerability falls under CWE-125, which describes out-of-bounds read conditions that occur when a program attempts to access memory beyond the allocated buffer limits. The attack vector is particularly concerning as it requires no authentication or user interaction beyond the simple act of opening or scanning the malicious pdf file, making it a significant threat to organizations relying on ClamAV for email and file scanning operations.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged by threat actors to create targeted denial of service attacks against systems running vulnerable ClamAV versions. When exploited, the out-of-bounds read condition causes the ClamAV daemon to terminate unexpectedly, leading to complete scanning failures for pdf files and potentially affecting broader network security operations. Organizations may experience cascading effects where email systems, file servers, and network traffic monitoring tools that depend on ClamAV for pdf analysis become temporarily or permanently unavailable. The vulnerability's remote exploitation capability means that attackers can deliver malicious pdf files through various channels including email attachments, web downloads, or file sharing platforms without requiring physical access to target systems. This characteristic aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how seemingly benign file processing functions can become weaponized attack vectors.
Mitigation strategies for CVE-2013-2021 should prioritize immediate version updates to ClamAV 0.97.8 or later, which includes patches specifically addressing the out-of-bounds read condition in the pdf.c module. System administrators should implement comprehensive patch management procedures to ensure all ClamAV installations are updated promptly, as the vulnerability affects a core scanning component used across numerous enterprise security solutions. Additional defensive measures include implementing strict file type filtering at network perimeters to block pdf files from entering critical systems, utilizing sandboxing techniques for pdf file analysis, and deploying multiple layers of security controls to reduce reliance on any single antivirus solution. Organizations should also consider implementing monitoring and alerting systems to detect unusual ClamAV daemon behavior or unexpected termination patterns that may indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of input validation in security-sensitive applications and the potential for memory safety issues to create significant operational disruptions in enterprise security infrastructure.