Critical vulnerability in WinRAR exposed

A remote code execution vulnerability has been reported in WinRAR, exposing 500 million users to a possible attack. The vulnerability is due to improper handling of the relative path of a file in an ACE archive, which leads to directory traversal. A remote attacker could exploit this vulnerability by enticing a target user to open a maliciously crafted ACE file. Successful exploitation of the vulnerability could lead to arbitrary code execution in the context of the user.

WinRAR:

WinRAR from RARLAB is a popular file-archiving utility for Windows, which can create and allow viewing of archives in RAR data archive compression format. It can also unpack files of multiple third party formats, such as ZIP, ACE, CAB, and so on.

CVE-2018-20250:

A path traversal vulnerability is reported in a third party dynamic link library, unacev2.dll. WinRAR makes use of this library for unpacking ACE archive files. ACE archive specifies an input file path into which files gets extracted. While unpacking ACE files, input file path gets validated. However, the current validation can be bypassed by tweaking the file path, allowing path traversal attacks. An attacker can craft a ACE archive file, disguised as a RAR file, that when opened by WinRAR, exploits a path traversal vulnerability in unacev2.dll to trick the archiving tool  into extracting files to an arbitrary path or to a computer’s startup folder (files that reside in the Startup folders get executed on every startup). 

Fix
Upgrade to the latest WinRAR version to resolve the issue
WinRAR prior to 5.70 beta 1 are affected by this vulnerability

SonicWall Threat Research Lab provides protection against this exploit with the following signatures:

SPY: 5408 Malformed-File ace.TL.1
SPY: 5411 File-Format ace

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