CVE-2021-42197
📋 TL;DR
CVE-2021-42197 is a memory leak vulnerability in swftools' swfdump utility that can lead to remote code execution. Attackers can exploit this by providing malicious SWF files to swfdump, potentially gaining control of affected systems. This affects all users of swftools through version 20201222.
💻 Affected Systems
- swftools
📦 What is this software?
Swftools by Swftools
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining root/administrator privileges and establishing persistent access.
Likely Case
Local privilege escalation or denial of service through memory exhaustion on systems processing untrusted SWF files.
If Mitigated
Limited impact if swfdump is not used or only processes trusted files, with potential for service disruption.
🎯 Exploit Status
Exploitation requires crafting malicious SWF files. Public GitHub issue demonstrates the vulnerability with sample files.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version after 20201222 (check latest release)
Vendor Advisory: https://github.com/matthiaskramm/swftools/issues/177
Restart Required: No
Instructions:
1. Check current swftools version: swfdump -v
2. Update to latest version from official repository
3. Recompile if using source distribution
4. Test with known safe SWF files
🔧 Temporary Workarounds
Disable swfdump usage
linuxRemove or restrict swfdump binary execution permissions
sudo chmod 000 /usr/bin/swfdump
sudo mv /usr/bin/swfdump /usr/bin/swfdump.disabled
Sandbox swfdump execution
linuxRun swfdump in isolated container or sandbox environment
docker run --rm -v $(pwd):/data alpine/swftools swfdump /data/file.swf
🧯 If You Can't Patch
- Implement strict input validation for SWF files before processing with swfdump
- Monitor system memory usage when swfdump processes files and kill processes exceeding thresholds
🔍 How to Verify
Check if Vulnerable:
Check swftools version: swfdump -v 2>&1 | head -1. If version is 20201222 or earlier, system is vulnerable.Check Version:
swfdump -v 2>&1 | grep -o 'swfdump [0-9].*'Verify Fix Applied:
Test with the proof-of-concept SWF file from GitHub issue #177. Fixed version should not crash or leak memory.📡 Detection & Monitoring
Log Indicators:
- swfdump process crashes
- Abnormal memory consumption by swfdump
- Repeated swfdump process spawns
Network Indicators:
- SWF file uploads to systems running swftools
- Unexpected outbound connections after SWF processing
SIEM Query:
process_name="swfdump" AND (event_id=1000 OR memory_usage>500MB)