CVE-2019-25677 Overview
CVE-2019-25677 is a denial of service vulnerability affecting WinRAR version 5.61. The vulnerability allows local attackers to crash the application by placing a malformed winrar.lng language file in the installation directory. When a user opens an archive and presses the test button, the application attempts to read invalid data, causing an access violation at memory address 004F1DB8 and resulting in an application crash.
Critical Impact
Local attackers can reliably crash WinRAR by manipulating language configuration files, disrupting user productivity and potentially enabling further attacks during the denial of service condition.
Affected Products
- RARLab WinRAR 5.61 (x86)
- Windows systems with WinRAR installed with writable installation directories
Discovery Timeline
- 2026-04-05 - CVE-2019-25677 published to NVD
- 2026-04-09 - Last updated in NVD database
Technical Details for CVE-2019-25677
Vulnerability Analysis
This vulnerability is classified under CWE-379 (Creation of Temporary File in Directory with Insecure Permissions). The core issue stems from WinRAR's failure to properly validate the contents of its language file (winrar.lng) before processing. When the application loads a maliciously crafted language file containing invalid or corrupted data structures, it fails to handle the unexpected input gracefully.
The vulnerability specifically manifests when a user performs archive testing operations. During this process, WinRAR reads string resources from the language file to display status messages. If the language file contains malformed data that doesn't conform to expected format specifications, the application encounters an access violation when attempting to dereference invalid memory locations.
Root Cause
The root cause lies in insufficient input validation when parsing the winrar.lng language file. WinRAR trusts the integrity of files within its installation directory without performing adequate bounds checking or data validation. When the application encounters a malformed language file, it attempts to read data from an invalid memory location, triggering the access violation at address 004F1DB8.
This represents a classic case of improper handling of untrusted file contents within an application's configuration system. The language file parser lacks defensive programming measures to detect and reject malformed input before it causes memory access errors.
Attack Vector
The attack requires local access to the target system with write permissions to the WinRAR installation directory. An attacker must:
- Gain write access to the WinRAR installation folder (typically C:\Program Files\WinRAR\ or C:\Program Files (x86)\WinRAR\)
- Replace or modify the legitimate winrar.lng file with a malformed version
- Wait for a user to open any archive and click the "Test" button
- The application will crash with an access violation, denying service
This attack vector limits exploitation to scenarios where an attacker already has local system access with elevated privileges or where directory permissions are misconfigured to allow non-privileged write access.
For detailed technical information about this vulnerability, refer to the Exploit-DB #46432 entry and the VulnCheck WinRAR DoS Advisory.
Detection Methods for CVE-2019-25677
Indicators of Compromise
- Presence of modified or recently changed winrar.lng files in the WinRAR installation directory
- WinRAR application crash events with access violation at memory address 004F1DB8
- Unexpected changes to files within the WinRAR installation folder
- Windows Event Log entries indicating WinRAR.exe crashes
Detection Strategies
- Monitor file integrity of the WinRAR installation directory, particularly the winrar.lng file
- Implement application crash monitoring to detect repeated WinRAR access violations
- Deploy endpoint detection rules to alert on modifications to application language files
- Establish baseline hashes for legitimate WinRAR installation files and alert on deviations
Monitoring Recommendations
- Configure File Integrity Monitoring (FIM) for the WinRAR installation directory
- Enable Windows Application Event Log monitoring for WinRAR crash events
- Monitor for unusual file write operations targeting program installation directories
- Implement user behavior analytics to detect insider threat scenarios
How to Mitigate CVE-2019-25677
Immediate Actions Required
- Upgrade WinRAR to the latest available version from the official WinRAR download page
- Review and restrict write permissions on the WinRAR installation directory
- Implement application whitelisting to prevent unauthorized file modifications
- Consider removing unnecessary language files if not required for multi-language support
Patch Information
RARLab has released newer versions of WinRAR that address this and other security issues. Organizations should upgrade from version 5.61 to the latest stable release. Refer to the official RARLab website for current version information and download links.
Workarounds
- Restrict NTFS permissions on the WinRAR installation directory to prevent non-administrator modifications
- Implement Software Restriction Policies or AppLocker rules to protect installation directories
- Consider using alternative archive utilities in high-security environments until upgrades are complete
- Deploy endpoint protection solutions capable of detecting file tampering in protected directories
# Configuration example - Restrict WinRAR directory permissions
icacls "C:\Program Files\WinRAR" /inheritance:r /grant:r Administrators:(OI)(CI)F /grant:r "SYSTEM":(OI)(CI)F /grant:r Users:(OI)(CI)RX
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
