CVE-2021-28835
📋 TL;DR
A buffer overflow vulnerability in XNView allows local attackers to execute arbitrary code by opening a specially crafted GEM bitmap file. This affects users running XNView versions before 2.50. Attackers could gain full control of the system if successful.
💻 Affected Systems
- XNView
📦 What is this software?
Xnview by Xnview
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with arbitrary code execution leading to data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Local privilege escalation or malware execution in the context of the user running XNView.
If Mitigated
Limited impact if application runs with minimal privileges and in isolated environments.
🎯 Exploit Status
Requires user interaction to open malicious file. No public exploit code identified.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.50 and later
Vendor Advisory: https://newsgroup.xnview.com/viewtopic.php?f=35&t=44679
Restart Required: No
Instructions:
1. Download XNView 2.50 or later from https://www.xnview.com/en/xnview/. 2. Install the update. 3. Verify version is 2.50 or higher.
🔧 Temporary Workarounds
Disable GEM bitmap file association
allRemove file association for .gem files to prevent automatic opening with XNView
Windows: Use 'Default Programs' settings to change .gem file association
Linux/macOS: Remove .gem from XNView's supported file types in configuration
Restrict file access
allBlock opening of untrusted GEM bitmap files
🧯 If You Can't Patch
- Run XNView with minimal user privileges to limit impact of exploitation
- Implement application whitelisting to prevent execution of unauthorized code
🔍 How to Verify
Check if Vulnerable:
Check XNView version in Help > About. If version is below 2.50, system is vulnerable.Check Version:
Windows: xnview.exe --version or check in Help > About. Linux/macOS: xnview --versionVerify Fix Applied:
Confirm version is 2.50 or higher in Help > About menu.📡 Detection & Monitoring
Log Indicators:
- Application crashes when opening GEM files
- Unexpected process execution from XNView
Network Indicators:
- Unusual outbound connections from XNView process
SIEM Query:
Process creation where parent process contains 'xnview' and command line contains suspicious parameters