CVE-2010-1639 in ClamAV
Summary
by MITRE
The cli_pdf function in libclamav/pdf.c in ClamAV before 0.96.1 allows remote attackers to cause a denial of service (crash) via a malformed PDF file, related to an inconsistency in the calculated stream length and the real stream length.
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Analysis
by VulDB Data Team • 09/14/2021
The vulnerability identified as CVE-2010-1639 represents a critical denial of service flaw within ClamAV's PDF processing capabilities. This issue affects ClamAV versions prior to 0.96.1 and specifically targets the cli_pdf function located in the libclamav/pdf.c source file. The flaw manifests when the antivirus engine encounters malformed PDF files that contain inconsistencies between calculated and actual stream lengths within the document structure. This particular vulnerability falls under the category of software defects that can be exploited to disrupt service availability rather than to gain unauthorized access or execute malicious code.
The technical root cause of this vulnerability stems from inadequate input validation within the PDF parsing logic of ClamAV. When processing PDF documents, the cli_pdf function performs calculations to determine the expected length of data streams within the file. However, when confronted with PDF files containing malformed stream length specifications, the system fails to properly handle the discrepancy between the calculated stream length and the actual stream length present in the document. This inconsistency creates a condition where the parser attempts to access memory or process data in ways that lead to program termination or crash. The vulnerability demonstrates a classic buffer over-read or memory access violation scenario that can be triggered through carefully crafted PDF content.
From an operational perspective, this vulnerability poses significant risks to organizations relying on ClamAV for email and file scanning operations. Attackers can exploit this flaw by simply sending specially crafted PDF attachments to systems running vulnerable ClamAV versions, causing the antivirus software to crash and potentially rendering the system unable to process further files until the service is manually restarted. The impact extends beyond simple service disruption as it can be leveraged in larger attack campaigns where multiple systems are targeted simultaneously, leading to cascading failures in network security infrastructure. This vulnerability particularly affects email security appliances, network firewalls, and endpoint protection systems that utilize ClamAV for content inspection.
The mitigation strategy for CVE-2010-1639 involves immediate deployment of ClamAV version 0.96.1 or later, which includes patches addressing the stream length validation inconsistencies. Organizations should also implement additional protective measures such as deploying PDF file scanning bypass mechanisms for suspicious content, implementing multiple layers of security validation, and maintaining regular updates to antivirus signatures. From a cybersecurity framework perspective, this vulnerability aligns with CWE-125: Out-of-bounds Read and CWE-248: Uncaught Exception categories, demonstrating the importance of proper error handling and input validation. The flaw also relates to ATT&CK technique T1059.007: Command and Scripting Interpreter: Python, as it can be exploited through automated delivery mechanisms that target vulnerable systems. Organizations should consider implementing network segmentation and content filtering to prevent exploitation attempts while awaiting patch deployment, particularly in environments where immediate updates may not be feasible due to operational constraints or compatibility concerns.