CVE-2015-7697 in UnZip
Summary
by MITRE
Info-ZIP UnZip 6.0 allows remote attackers to cause a denial of service (infinite loop) via empty bzip2 data in a ZIP archive.
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Analysis
by VulDB Data Team • 06/25/2022
The vulnerability identified as CVE-2015-7697 affects Info-ZIP UnZip version 6.0 and represents a denial of service weakness that can be exploited remotely through specially crafted ZIP archive files containing empty bzip2 data. This issue stems from the decompression routine's inadequate handling of malformed bzip2 compressed data streams, creating a condition where the decompression process enters an infinite loop when encountering empty or malformed bzip2 data within archive entries. The flaw manifests specifically during the extraction process when UnZip attempts to decompress bzip2-compressed content that lacks proper data structure or contains zero-length compressed data segments.
From a technical perspective, this vulnerability operates at the decompression layer of the UnZip utility where bzip2 data streams are processed. When the decompression engine encounters empty bzip2 data, it fails to properly validate the data structure and instead continues processing in a loop that never terminates. This behavior aligns with CWE-835, which describes the weakness of infinite loops or iterations that do not have proper exit conditions. The vulnerability is particularly concerning because it can be triggered through standard ZIP archive extraction operations without requiring special privileges or complex attack vectors, making it accessible to remote attackers who can simply provide a malicious ZIP file.
The operational impact of this vulnerability extends beyond simple service disruption as it can affect any system running UnZip 6.0 when processing untrusted archive files. The infinite loop condition consumes system resources continuously, potentially leading to system instability, resource exhaustion, and denial of service for legitimate users. This weakness is especially dangerous in automated environments where ZIP files are processed without user intervention, such as in web applications, email systems, or automated backup solutions. The vulnerability affects the availability aspect of the system by preventing normal operation and can be exploited in scenarios where attackers can influence the archive content being processed.
Mitigation strategies for CVE-2015-7697 should focus on immediate software updates to versions that address the bzip2 decompression handling issue, as well as implementing proper input validation and resource monitoring. Organizations should consider deploying automated patch management systems to ensure timely updates across all affected systems. Additionally, implementing sandboxing techniques for archive processing, setting resource limits on decompression operations, and employing signature-based detection for known malicious ZIP files can provide layered defense. The ATT&CK framework categorizes this vulnerability under T1499.004 for Network Denial of Service, highlighting the importance of proper input validation and resource management in preventing such attacks. System administrators should also consider implementing network-based intrusion detection systems that can identify and block suspicious archive processing activities that may indicate exploitation attempts.