CVE-2023-40477: Rarlab WinRAR RCE Vulnerability

CVE-2023-40477 Overview

CVE-2023-40477 is a high-severity remote code execution vulnerability affecting RARLAB WinRAR, one of the most widely used file archiving utilities. This vulnerability allows remote attackers to execute arbitrary code on affected installations through improper validation of array index in recovery volume processing. User interaction is required to exploit this vulnerability—the target must visit a malicious page or open a malicious file.

The specific flaw exists within the processing of recovery volumes. The issue results from the lack of proper validation of user-supplied data, which can result in a memory access past the end of an allocated buffer (CWE-129: Improper Validation of Array Index). An attacker can leverage this vulnerability to execute code in the context of the current process.

Critical Impact

Successful exploitation allows attackers to execute arbitrary code with the privileges of the current user, potentially leading to complete system compromise when users open maliciously crafted RAR archives.

Affected Products

• RARLAB WinRAR (versions prior to security patch)
• Systems running WinRAR for processing RAR recovery volumes
• Debian Linux systems with WinRAR packages

Discovery Timeline

• 2024-05-03 - CVE CVE-2023-40477 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2023-40477

Vulnerability Analysis

This vulnerability stems from improper validation of array index during the processing of RAR recovery volumes. When WinRAR processes a specially crafted recovery volume file, it fails to properly validate user-supplied data before using it as an array index. This oversight allows an attacker to reference memory locations outside the intended buffer boundaries.

The vulnerability was tracked internally as ZDI-CAN-21233 and was publicly disclosed through the Zero Day Initiative Advisory ZDI-23-1152. The local attack vector requires user interaction, meaning an attacker must convince a user to open a malicious archive file or visit a webpage that triggers the vulnerable code path.

Root Cause

The root cause is an Improper Validation of Array Index (CWE-129) vulnerability in WinRAR's recovery volume processing functionality. The application does not adequately verify that array index values derived from user-supplied data fall within the valid bounds of allocated memory buffers. This allows crafted input to cause memory access past the end of an allocated buffer, corrupting adjacent memory regions.

Attack Vector

The attack requires local access with user interaction. An attacker would typically:

1. Craft a malicious RAR archive with a specially constructed recovery volume
2. Distribute the malicious archive via email attachments, malicious websites, or other file-sharing methods
3. Social engineer the victim into opening the archive with WinRAR
4. Upon processing the recovery volume, WinRAR accesses memory beyond allocated boundaries
5. The attacker gains code execution in the context of the current process

The vulnerability leverages the lack of bounds checking to achieve an out-of-bounds memory access, which can be weaponized to execute arbitrary code. Since WinRAR typically runs with user-level privileges, successful exploitation grants the attacker the same access level as the victim user.

Detection Methods for CVE-2023-40477

Indicators of Compromise

• Unusual process behavior from WinRAR.exe or Rar.exe including unexpected child processes or network connections
• RAR archives with malformed recovery volume structures (.rev files)
• Memory access violations or application crashes when opening RAR archives
• Presence of suspicious RAR files received via email or downloaded from untrusted sources

Detection Strategies

• Monitor for unexpected code execution originating from WinRAR process contexts
• Implement file integrity monitoring on systems where WinRAR is installed to detect unauthorized modifications
• Deploy endpoint detection solutions that can identify exploitation attempts targeting memory corruption vulnerabilities
• Enable application crash logging and analyze WinRAR crash dumps for exploitation indicators

Monitoring Recommendations

• Configure security solutions to inspect RAR archive contents before user interaction
• Monitor for anomalous WinRAR process behavior including unusual memory allocation patterns
• Implement email gateway scanning to detect potentially malicious RAR attachments
• Deploy SentinelOne Singularity to provide real-time behavioral analysis and prevent exploitation attempts

How to Mitigate CVE-2023-40477

Immediate Actions Required

• Update WinRAR to the latest patched version immediately
• Restrict handling of RAR files from untrusted sources until patches are applied
• Educate users about the risks of opening archives from unknown senders
• Consider temporarily blocking .rev (recovery volume) files at email gateways and web proxies

Patch Information

RARLAB has released a security update to address this vulnerability. Organizations should immediately update WinRAR installations to the latest available version. Refer to the WinRAR Security Update for detailed patch information and download links.

For Debian-based Linux systems, refer to the Debian LTS Announcement for package update instructions.

Workarounds

• Use alternative archive utilities that are not affected by this vulnerability until WinRAR can be patched
• Implement application whitelisting to prevent unauthorized code execution from WinRAR context
• Configure email security gateways to quarantine RAR files with recovery volumes
• Deploy endpoint protection solutions like SentinelOne that can detect and block exploitation attempts in real-time

# Configuration example
# Verify WinRAR version on Windows systems
# Check installed version via registry
reg query "HKLM\SOFTWARE\WinRAR" /v "exe64"
reg query "HKLM\SOFTWARE\WOW6432Node\WinRAR" /v "exe32"

# For Debian/Ubuntu systems, update WinRAR packages
sudo apt update
sudo apt upgrade unrar-free