CVE-2015-2668 in Clam
Summary
by MITRE
ClamAV before 0.98.7 allows remote attackers to cause a denial of service (infinite loop) via a crafted xz archive file.
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Analysis
by VulDB Data Team • 05/10/2022
The vulnerability identified as CVE-2015-2668 represents a critical denial of service flaw in ClamAV versions prior to 0.98.7, specifically targeting the xz compression format handling mechanism. This issue arises from insufficient input validation and improper state management within the decompression routines, creating a condition where maliciously crafted xz archive files can trigger an infinite loop during processing. The flaw exists in the decompression logic that fails to properly terminate loop iterations when encountering malformed or specially constructed xz archives, leading to resource exhaustion and system unresponsiveness.
The technical implementation of this vulnerability stems from the xz decompression library integration within ClamAV's file scanning framework. When ClamAV encounters an xz archive, it employs a decompression algorithm that processes the archive header and subsequent data blocks. The vulnerability manifests when the archive contains malformed data structures that cause the decompression loop to iterate indefinitely without proper termination conditions. This behavior aligns with CWE-835, which specifically addresses the issue of infinite loops in software implementations. The flaw demonstrates poor defensive programming practices where boundary conditions and input validation checks are insufficient to handle malformed data sequences.
From an operational perspective, this vulnerability presents significant risks to organizations relying on ClamAV for email filtering, file scanning, and endpoint protection. Attackers can exploit this weakness by sending specially crafted xz archive files through email attachments, file uploads, or network transfers, causing ClamAV processes to enter infinite loops and consume excessive CPU resources. The impact extends beyond simple service disruption as the infinite loop can lead to complete system resource exhaustion, potentially affecting other security services and system functionality. This vulnerability directly maps to ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how seemingly benign file formats can be weaponized for system disruption.
The exploitation of CVE-2015-2668 requires minimal technical sophistication from attackers, as they only need to create or obtain xz archives with specific malformed structures to trigger the vulnerability. The affected ClamAV versions lack proper input sanitization and timeout mechanisms during decompression operations, making the system vulnerable to both intentional attacks and accidental resource exhaustion. Organizations using older ClamAV versions face substantial risk as this flaw can be leveraged in various attack scenarios including spam campaigns, file upload attacks, and system reconnaissance activities. The vulnerability's impact is amplified in environments where ClamAV operates as a central security component, as it can effectively disable critical threat detection capabilities while consuming system resources. Mitigation strategies must include immediate version upgrades to ClamAV 0.98.7 or later, implementation of proper input validation at network boundaries, and deployment of additional monitoring to detect anomalous resource consumption patterns that may indicate exploitation attempts.