CVE-2021-42199
📋 TL;DR
This CVE describes a heap buffer overflow vulnerability in swftools that allows remote code execution when processing malicious SWF files. Attackers can exploit this by tricking users into opening specially crafted SWF files, potentially compromising systems running vulnerable versions of swftools. The vulnerability 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 complete control over the affected system, enabling data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Local privilege escalation or arbitrary code execution in the context of the user running swftools, potentially leading to lateral movement within networks.
If Mitigated
Limited impact with proper sandboxing and least privilege principles, potentially only crashing the swftools process without code execution.
🎯 Exploit Status
Exploitation requires the victim to process a malicious SWF file. The GitHub issue includes technical details that could facilitate exploit development.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version after 20201222 (check latest release)
Vendor Advisory: https://github.com/matthiaskramm/swftools/issues/173
Restart Required: No
Instructions:
1. Check current swftools version. 2. Update to latest version from official repository. 3. Recompile if using source distribution. 4. Test with known safe SWF files to ensure functionality.
🔧 Temporary Workarounds
Disable SWF processing
linuxTemporarily disable swftools or block SWF file processing until patching is complete
sudo systemctl stop swftools
sudo chmod 000 /usr/bin/swftools
Sandbox execution
allRun swftools in a container or sandboxed environment to limit potential damage
docker run --rm -v $(pwd):/data swftools-container
🧯 If You Can't Patch
- Implement strict input validation to reject untrusted SWF files
- Deploy application allowlisting to prevent unauthorized swftools execution
🔍 How to Verify
Check if Vulnerable:
Check swftools version: swftools --version | grep -i versionCheck Version:
swftools --versionVerify Fix Applied:
Verify version is newer than 20201222 and test processing known safe SWF files📡 Detection & Monitoring
Log Indicators:
- Segmentation fault or crash logs from swftools process
- Unusual memory allocation patterns in system logs
Network Indicators:
- Unexpected outbound connections from swftools process
- File uploads containing SWF files to web applications
SIEM Query:
process_name:"swftools" AND (event_type:"crash" OR memory_usage:"spike")