CVE-2017-6420 in ClamAV
Summary
by MITRE
The wwunpack function in libclamav/wwunpack.c in ClamAV 0.99.2 allows remote attackers to cause a denial of service (use-after-free) via a crafted PE file with WWPack compression.
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Analysis
by VulDB Data Team • 12/15/2022
The vulnerability identified as CVE-2017-6420 resides within the ClamAV antivirus engine's libclamav library, specifically in the wwunpack function located in the libclamav/wwunpack.c file. This flaw affects ClamAV version 0.99.2 and represents a critical use-after-free vulnerability that can be exploited remotely through the processing of maliciously crafted PE files containing WWPack compression. The vulnerability stems from improper memory management during the decompression process of compressed PE files, creating a scenario where freed memory locations are accessed after being deallocated.
The technical implementation of this vulnerability involves the wwunpack function failing to properly validate or handle the memory allocation and deallocation sequence when processing WWPack compressed data within PE files. When a malicious PE file with crafted WWPack compression is processed by ClamAV, the function executes code that leads to a use-after-free condition. This occurs because the function allocates memory for decompression operations but does not adequately verify the integrity of the compressed data or properly manage the memory lifecycle. The freed memory pointer is subsequently accessed during further processing, leading to unpredictable behavior that can result in application crashes or system instability.
The operational impact of this vulnerability extends beyond simple denial of service, as it provides remote attackers with a potential vector for more sophisticated attacks. The use-after-free condition can be leveraged by attackers to potentially execute arbitrary code or escalate privileges within the system running the vulnerable ClamAV service. This represents a significant security risk for organizations relying on ClamAV for malware detection, as the vulnerability can be triggered through normal file scanning operations without requiring user interaction or special privileges. The remote exploitation capability means that attackers can craft malicious PE files and deliver them through various attack vectors, including email attachments, web downloads, or file sharing platforms, making the vulnerability particularly dangerous in enterprise environments.
Mitigation strategies for CVE-2017-6420 should prioritize immediate patching of affected ClamAV installations to version 0.99.3 or later, which contains the necessary fixes for the memory management issues. Organizations should also implement additional protective measures such as network segmentation to limit the exposure of ClamAV services, deploying file scanning rules that restrict execution of compressed files from untrusted sources, and maintaining comprehensive monitoring of system stability and performance metrics. Security teams should consider implementing sandboxing mechanisms for suspicious file analysis and establish incident response procedures specifically addressing use-after-free vulnerabilities. The vulnerability aligns with CWE-416, which describes the use of freed memory condition, and represents a typical example of how improper memory management can create remote exploitation opportunities. From an ATT&CK perspective, this vulnerability maps to techniques involving execution of malicious code through file processing and can be categorized under the T1059.007 sub-technique for scripting and T1203 for exploitation of remote services, making it a critical concern for defensive security operations.