CVE-2007-3726 in unrar
Summary
by MITRE
Integer signedness error in the SET_VALUE function in rarvm.cpp in unrar 3.70 beta 3, as used in products including WinRAR and RAR for OS X, allows user-assisted remote attackers to cause a denial of service (crash) via a crafted RAR archive that causes a negative signed number to be cast to a large unsigned number.
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Analysis
by VulDB Data Team • 09/05/2018
The vulnerability described in CVE-2007-3726 represents a critical integer signedness error within the rarvm.cpp component of unrar version 3.70 beta 3, which forms the core decompression engine for several widely-used archiving applications including WinRAR and RAR for OS X. This flaw exists within the SET_VALUE function where the software fails to properly handle the conversion between signed and unsigned integer representations during RAR archive processing. The vulnerability is classified under CWE-191 as an Integer Underflow (Wrap or Wraparound) and demonstrates a classic example of how improper handling of integer types can lead to exploitable conditions in archive processing software.
The technical implementation of this vulnerability occurs when a maliciously crafted RAR archive contains specially constructed data that triggers the SET_VALUE function to process a negative signed integer value. During the normal execution flow, this negative value gets cast to an unsigned integer type, resulting in an extremely large positive number due to the mathematical properties of two's complement representation. This conversion creates a scenario where the unsigned integer becomes so large that it exceeds the bounds of valid memory allocations or array indexing operations within the decompression engine. The flaw is particularly dangerous because it can be triggered remotely through user-assisted means, requiring only that a victim open or process the malicious archive file.
The operational impact of this vulnerability manifests as a denial of service condition that results in application crashes and system instability. When the malicious archive is processed by affected software, the integer overflow causes memory corruption that leads to segmentation faults or access violations, ultimately terminating the application process. This behavior affects not only the individual user experience but also represents a potential vector for more sophisticated attacks if the vulnerability can be chained with other exploits. The vulnerability affects a broad range of products since WinRAR and RAR for OS X both utilize the same unrar library components, making the impact widespread across multiple operating systems and platforms.
Security professionals should recognize this vulnerability as a prime example of how seemingly minor coding errors in low-level system components can result in significant security implications. The flaw demonstrates the importance of proper input validation and integer type handling in archive processing software, particularly when dealing with untrusted data from external sources. Mitigation strategies should include immediate patching of affected versions to the latest stable releases of unrar and related applications, implementation of proper input sanitization measures, and deployment of network-based intrusion detection systems that can identify and block malicious RAR archive traffic. Additionally, users should be educated about the risks of opening archives from untrusted sources and organizations should consider implementing automated malware scanning for archive files in their security protocols. This vulnerability serves as a reminder of the critical importance of proper integer handling in security-sensitive applications and aligns with ATT&CK technique T1059.007 for execution through archive files.