WinRAR Zero-Day Exploited by RomCom Hackers: When Archive Tools Become Attack Vectors

A recently patched WinRAR vulnerability (CVE-2025-8088) was exploited as a zero-day by the RomCom hacking group in sophisticated phishing attacks, demonstrating how attackers are increasingly targeting common software tools that users trust implicitly. This incident highlights the growing threat of supply chain attacks and the importance of prompt software updates.

The WinRAR Vulnerability Overview

CVE-2025-8088 is a critical directory traversal vulnerability that affects multiple WinRAR components across different platforms. The flaw allows specially crafted archives to extract files into arbitrary locations on the victim's system, bypassing user-specified extraction paths. (CVE-2025-8088)

Key Details:

• Vulnerability: CVE-2025-8088 (Directory Traversal)
• Affected Products: WinRAR, Windows RAR, UnRAR, portable UnRAR source code, UnRAR.dll
• Attack Vector: Maliciously crafted RAR archives
• Impact: Remote code execution through autorun mechanisms
• Status: Fixed in WinRAR 7.13 (August 2025)

Affected Systems:

• Windows versions of RAR, UnRAR, portable UnRAR source code, and UnRAR.dll
• Unix versions are NOT affected
• RAR for Android is NOT affected

How the Vulnerability Works

The vulnerability exploits WinRAR's file extraction mechanism:

Technical Mechanism:

1. Path Manipulation: Attackers create archives with specially crafted file paths
2. Directory Traversal: The extraction process follows malicious path instructions
3. Arbitrary File Placement: Files are extracted to unauthorized locations
4. Autorun Exploitation: Executables placed in startup folders for persistence

Attack Process:

1. Archive Creation: Attacker creates RAR file with malicious path structure
2. Phishing Delivery: Archive sent via email or other delivery methods
3. User Extraction: Victim extracts the archive using vulnerable WinRAR version
4. Silent Installation: Malicious files placed in autorun locations
5. Persistent Execution: Malware runs automatically on next system startup

Autorun Locations Targeted:

• %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup (User-specific)
• %ProgramData%\Microsoft\Windows\Start Menu\Programs\StartUp (Machine-wide)

RomCom's Zero-Day Exploitation

ESET researchers Anton Cherepanov, Peter Košinár, and Peter Strýček discovered that the RomCom hacking group was actively exploiting this vulnerability before it was publicly disclosed.

RomCom Group Profile:

• Also Known As: Storm-0978, Tropical Scorpius, UNC2596
• Attribution: Russian-aligned threat actor
• Capabilities: Ransomware, data theft, credential harvesting
• Targets: Government, healthcare, technology sectors

Attack Methodology:

1. Spearphishing Campaigns: Targeted emails with malicious RAR attachments
2. Zero-Day Exploitation: Used vulnerability before public disclosure
3. RomCom Backdoor: Deployed custom malware for persistence
4. Data Exfiltration: Stole credentials and sensitive information

Historical Context:

RomCom has been linked to numerous ransomware operations including:

• Cuba ransomware campaigns
• Industrial Spy data theft operations
• Multiple zero-day exploits in various software

Enterprise Security Implications

Supply Chain Attack Vector:

This incident demonstrates how attackers are targeting:

• Common software tools that users trust implicitly
• Legitimate software with wide deployment
• Software without auto-update mechanisms
• Tools used in business processes

Risk Factors:

• Mass Deployment: WinRAR is widely used in enterprise environments
• Manual Updates: No automatic update mechanism increases vulnerability window
• Trust Exploitation: Users trust archive files from legitimate sources
• Persistence Mechanism: Autorun placement ensures long-term access

Compliance Impact:

Organizations with SOC 2, ISO 27001, or other compliance requirements may face:

• Control failures in software management
• Incident response obligations for zero-day exploitation
• Vendor management gaps for software security
• Supply chain security control deficiencies

Detection and Response

Indicators of Compromise:

• Suspicious RAR files in email attachments
• Unexpected files in startup directories
• RomCom backdoor artifacts in system memory
• Unusual network connections to command and control servers

Immediate Actions:

1. Update WinRAR to version 7.13 or later immediately
2. Scan for RomCom indicators in affected systems
3. Review startup directories for unauthorized executables
4. Monitor for suspicious network activity

Long-term Prevention:

1. Implement software inventory and update management
2. Deploy email security with attachment scanning
3. Use application whitelisting for autorun locations
4. Implement network segmentation and monitoring

The Broader Threat Landscape

Zero-Day Exploitation Trends:

• Increasing frequency of zero-day discoveries
• Shorter exploitation windows between disclosure and attacks
• Targeting of common software with wide deployment
• Supply chain focus on trusted tools and platforms

Archive File Security:

• Archive formats becoming popular attack vectors
• Compression tools targeted for vulnerabilities
• File extraction processes exploited for persistence
• Trust in archive files being weaponized

Phishing Evolution:

• Sophisticated delivery methods using trusted file formats
• Zero-day integration into phishing campaigns
• Multi-stage attacks combining multiple vulnerabilities
• Persistence mechanisms through autorun exploitation

Vendor Response and Recommendations

WinRAR's Response:

• Timely patch release (version 7.13)
• Clear vulnerability disclosure
• Comprehensive changelog explaining the fix
• User notification of critical security update

User Recommendations:

1. Update immediately to WinRAR 7.13 or later
2. Verify download sources (win-rar.com only)
3. Implement software update policies
4. Train users on archive file security risks

Enterprise Recommendations:

1. Deploy centralized software management
2. Implement email security controls
3. Monitor for suspicious archive files
4. Have incident response plans for zero-day exploitation

Lessons Learned

Software Trust Model:

• No software is inherently safe from vulnerabilities
• Common tools are increasingly targeted
• Manual update processes create security gaps
• Trust in file formats can be exploited

Supply Chain Security:

• Vendor security practices must be verified
• Software update mechanisms are critical
• Incident response planning essential for zero-days
• Monitoring and detection capabilities required

User Education:

• Archive file risks need to be communicated
• Update importance must be emphasized
• Phishing awareness includes file attachment risks
• Security hygiene applies to all software tools

Immediate Action Steps

For All Users:

1. Update WinRAR to version 7.13 immediately
2. Scan systems for RomCom indicators
3. Review startup directories for unauthorized files
4. Monitor for suspicious activity

For Organizations:

1. Deploy WinRAR updates across all systems
2. Implement email security with attachment scanning
3. Update incident response procedures for zero-days
4. Train staff on archive file security risks

For Security Teams:

1. Monitor for RomCom indicators in your environment
2. Review software inventory and update procedures
3. Implement detection for suspicious archive files
4. Update threat intelligence with RomCom indicators

For organizations concerned about supply chain security, see our guide on Third-Party Risk Management: Best Practices. For companies evaluating their security posture, take our Compliance Posture Survey. For organizations looking to automate security monitoring, check out Building an AWS Audit Manager Solution in Under Two Days with Amazon Q.