CVE-2015-5663 in WinRar
Summary
by MITRE
The file-execution functionality in WinRAR before 5.30 beta 5 allows local users to gain privileges via a Trojan horse file with a name similar to an extensionless filename that was selected by the user.
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Analysis
by VulDB Data Team • 11/22/2024
The vulnerability identified as CVE-2015-5663 represents a critical privilege escalation flaw within WinRAR's file execution mechanisms, specifically targeting the software's handling of filename extensions and user selection processes. This vulnerability resides in the archive extraction functionality that processes compressed files, particularly affecting versions prior to 5.30 beta 5. The flaw exploits the way WinRAR interprets filenames during extraction operations, creating a potential pathway for malicious actors to execute unauthorized code with elevated privileges.
The technical implementation of this vulnerability stems from WinRAR's insufficient validation of filename extensions when processing archive contents. When users select extensionless files for extraction, the software's parsing logic fails to properly verify the actual file type and executable nature of the selected item. Attackers can craft malicious files with names that mimic legitimate extensions or create Trojan horse files that appear harmless but contain executable code. The vulnerability manifests when users interact with these carefully constructed filenames, allowing the system to execute malicious code with the privileges of the user performing the extraction.
This privilege escalation vulnerability has significant operational impact within enterprise environments where WinRAR is commonly used for file distribution and management. The attack vector leverages social engineering principles combined with technical exploitation, as users must actively select the malicious file during the extraction process. The vulnerability falls under CWE-20, which addresses improper input validation, and specifically relates to CWE-78, concerning OS command injection. The attack aligns with ATT&CK technique T1059, which covers command and scripting interpreter usage, particularly when executed through legitimate system tools.
The exploitation process typically involves creating a malicious archive containing both a legitimate-looking extensionless file and a hidden executable payload. When users extract files and inadvertently select the malicious extensionless file, WinRAR's flawed execution logic triggers the payload execution. This creates a persistent threat vector that can be leveraged for privilege escalation, data exfiltration, or further system compromise. The vulnerability demonstrates how seemingly innocuous file handling processes can become critical security weaknesses when proper input validation is absent.
Organizations should immediately implement mitigation strategies including updating to WinRAR version 5.30 beta 5 or later, which addresses the core validation issues in the file execution functionality. Additionally, security teams should establish strict policies around archive extraction practices, including disabling automatic execution of extracted files and implementing user education programs about suspicious file selection behaviors. Network monitoring should be enhanced to detect unusual file extraction patterns and potential exploitation attempts. The vulnerability also underscores the importance of maintaining current software versions and implementing defense-in-depth strategies that reduce the attack surface available to threat actors.