CVE-2018-20253 in WinRar
Summary
by MITRE
In WinRAR versions prior to and including 5.60, There is an out-of-bounds write vulnerability during parsing of a crafted LHA / LZH archive formats. Successful exploitation could lead to arbitrary code execution in the context of the current user.
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Analysis
by VulDB Data Team • 07/10/2023
The vulnerability identified as CVE-2018-20253 represents a critical out-of-bounds write flaw within WinRAR's archive parsing functionality, specifically affecting versions 5.60 and earlier. This vulnerability manifests during the processing of specially crafted LHA or LZH archive formats, which are legacy compression formats that WinRAR supports for backward compatibility. The flaw stems from insufficient input validation and boundary checking within the decompression routines that handle these specific archive types. When a maliciously constructed LHA/LZH archive is processed, the parsing logic fails to properly validate array bounds, leading to memory corruption that can be exploited by attackers. The vulnerability resides in the core decompression engine where the software attempts to write data beyond the allocated memory buffer, creating a condition that adversaries can leverage for code execution.
The technical implementation of this vulnerability aligns with CWE-129, which describes improper validation of array indices, and more specifically with CWE-787, which addresses out-of-bounds write conditions. Attackers can exploit this weakness by crafting a malicious archive file that contains malformed headers or compressed data structures that trigger the buffer overflow during extraction. The attack vector typically involves social engineering to convince users to open the malicious archive, as the vulnerability requires user interaction with the compromised file. When the vulnerable WinRAR application processes the crafted archive, it attempts to write data beyond the intended memory boundaries, potentially overwriting adjacent memory locations including function pointers, return addresses, or other critical program data. This memory corruption can result in arbitrary code execution with the privileges of the current user, making it particularly dangerous in enterprise environments where users may have elevated access rights.
The operational impact of CVE-2018-20253 extends beyond simple code execution, as it can enable attackers to establish persistent footholds within target systems. The vulnerability's exploitation does not require administrative privileges, making it particularly attractive to threat actors seeking initial access or lateral movement within networks. From an ATT&CK framework perspective, this vulnerability maps to techniques such as T1059.007 (Command and Scripting Interpreter: PowerShell) and T1203 (Exploitation for Client Execution) where adversaries can leverage the arbitrary code execution capability to deploy additional malware or establish command and control channels. The vulnerability's presence in WinRAR's legacy format support highlights the ongoing security risks associated with maintaining backward compatibility for outdated compression formats. Organizations running affected WinRAR versions face significant exposure since the flaw can be triggered through legitimate archive extraction processes, making detection and prevention challenging. The vulnerability demonstrates how legacy code support can introduce security weaknesses that persist across multiple software versions, particularly when older compression algorithms are implemented without modern security hardening practices.
Mitigation strategies for CVE-2018-20253 should prioritize immediate software updates to WinRAR version 5.61 or later, where the vulnerability has been patched. System administrators should implement comprehensive patch management processes to ensure all affected systems receive updates promptly. Additionally, organizations should consider implementing application whitelisting policies that restrict execution of WinRAR from untrusted sources and employ sandboxing techniques to isolate archive processing activities. Network-based protections such as intrusion detection systems can help detect attempts to deliver malicious archives through email or web-based attack vectors. Security teams should also conduct thorough vulnerability assessments to identify all systems running affected WinRAR versions and implement monitoring for suspicious archive processing activities. The remediation process must include user education to prevent social engineering attacks that rely on tricking users into opening malicious archives. Organizations should also consider migrating away from legacy compression formats when possible, as the continued support of older archive types increases the attack surface and introduces potential security risks that are difficult to fully address through patches alone.