CVE-2012-6706 in unrar
Summary
by MITRE
A VMSF_DELTA memory corruption was discovered in unrar before 5.5.5, as used in Sophos Anti-Virus Threat Detection Engine before 3.37.2 and other products, that can lead to arbitrary code execution. An integer overflow can be caused in DataSize+CurChannel. The result is a negative value of the "DestPos" variable, which allows the attacker to write out of bounds when setting Mem[DestPos].
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Analysis
by VulDB Data Team • 10/20/2019
The vulnerability identified as CVE-2012-6706 represents a critical memory corruption flaw within the RAR decompression library that affects multiple security products including Sophos Anti-Virus Threat Detection Engine. This issue stems from improper handling of integer overflow conditions during the decompression process, specifically within the VMSF_DELTA functionality that processes compressed data streams. The flaw manifests when processing specially crafted malicious RAR archives that trigger an integer overflow in the calculation involving DataSize and CurChannel parameters, leading to a cascading effect that compromises memory integrity.
The technical root cause of this vulnerability lies in the lack of proper input validation and integer overflow protection within the decompression algorithm. When the system processes a malformed RAR archive, the arithmetic operation DataSize+CurChannel results in an integer overflow that produces a negative value for the DestPos variable. This negative value subsequently gets used as an array index or memory offset, creating a classic out-of-bounds memory write condition. The vulnerability maps to CWE-190, Integer Overflow or Wraparound, and specifically demonstrates how improper integer handling can lead to memory corruption vulnerabilities. According to ATT&CK framework, this represents a code execution technique through memory corruption, falling under the T1059.007 execution method related to command and scripting interpreter.
The operational impact of this vulnerability extends beyond simple privilege escalation as it enables arbitrary code execution in the context of the decompression process, which typically runs with elevated privileges. Attackers can craft malicious RAR files that, when processed by affected systems, will trigger the integer overflow and subsequent memory corruption. This creates a remote code execution vector that can be exploited through various attack surfaces including email attachments, file downloads, and network-based file transfers. The vulnerability affects not just Sophos products but also other software that utilizes the unrar library, making it a widespread concern across multiple security vendors and endpoint protection solutions.
Mitigation strategies for CVE-2012-6706 should focus on immediate patching of affected software components, particularly the unrar library and Sophos Anti-Virus Threat Detection Engine versions prior to 3.37.2. Organizations should implement network-based intrusion detection systems to monitor for suspicious RAR file patterns and consider implementing sandboxing techniques for decompression operations. Additionally, security teams should establish strict file validation policies that include signature verification and behavioral analysis of decompressed content. The vulnerability demonstrates the importance of input validation and proper integer handling in security-critical code, highlighting the need for comprehensive code reviews and static analysis tools that can identify similar integer overflow patterns in legacy codebases. Organizations should also consider implementing network segmentation to limit the potential impact of exploitation and maintain regular vulnerability assessment programs to identify similar issues in third-party libraries and components.