Security Experts:

WinRAR Vulnerability Exposes Millions of Users to Attacks

WinRAR, the popular data compression tool utilized by over 500 million users worldwide, is affected by a serious vulnerability that can allow arbitrary code execution through specially crafted ACE archives.

Tests conducted by researchers at Check Point Software Technologies using the WinAFL fuzzer led to the discovery of a security bug in the unacev2.dll library used by WinRAR for unpacking ACE archives.

The library is affected by a flaw (CVE-2018-20250) that can allow malicious actors to create an ACE archive that extracts files to an arbitrary folder on the system.

Check Point researchers have demonstrated that the security hole can be exploited to extract a harmless file to the destination folder selected by the user, while also extracting a malicious file to a location specified by the attacker. The attacker could, for example, extract a piece of malware to the Windows Startup folder and it would get executed the next time the operating system boots.

The cybersecurity firm reported its findings to WinRAR developer RARLab, which decided that the best way to protect users against potential attacks is to remove support for ACE archives. This decision has been implemented starting with the release of WinRAR 5.70 beta 1.

RARLab says unacev2.dll has not been updated since 2005 and the company no longer has access to its source code.

The following CVE identifiers have been assigned to other WinRAR vulnerabilities found by Check Point during its fuzzing project: CVE-2018-20251, CVE-2018-20252 and CVE-2018-20253. The company has published technical details and a video showing an exploit in action.

The popularity of WinRAR can make it a tempting target for attackers. While no WinRAR vulnerabilities have been disclosed in the past three years, a flaw in the archiving tool was exploited in cyber espionage campaigns back in 2014.

WinRAR vulnerabilities are still valuable. Exploit acquisition firm Zerodium offers up to $80,000 for remote code execution flaws and at one point last year it offered as much as $100,000.

Related: Critical Vulnerability Addressed in Popular Code Libraries

Related: Microsoft Patches Code Execution Vulnerability in wimgapi Library

Related: CTB-Locker Ransomware Impersonator Uses WinRAR for Encryption

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.