CVE-2021-39574
📋 TL;DR
This vulnerability is a heap buffer overflow in swftools' pool_read() function that allows attackers to execute arbitrary code. It affects all users of swftools through version 20200710 who process untrusted SWF files. Successful exploitation could lead to complete system compromise.
💻 Affected Systems
- swftools
📦 What is this software?
Swftools by Swftools
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the swftools process, potentially leading to full system compromise, data theft, or ransomware deployment.
Likely Case
Local privilege escalation or denial of service when processing malicious SWF files, potentially leading to system instability or unauthorized access.
If Mitigated
Contained impact within isolated environments with proper sandboxing, minimal privileges, and network segmentation.
🎯 Exploit Status
Proof of concept exists in GitHub issue #124. Exploitation requires crafting a malicious SWF file that triggers the heap overflow during parsing.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 20200710
Vendor Advisory: https://github.com/matthiaskramm/swftools/issues/124
Restart Required: No
Instructions:
1. Update swftools to the latest version from the official repository. 2. Recompile from source if using self-compiled versions. 3. Replace any vulnerable binaries with patched versions.
🔧 Temporary Workarounds
Disable SWF processing
linuxTemporarily disable swftools processing of SWF files until patching is complete
# Remove execute permissions from swftools binaries
chmod -x /usr/bin/swftools
Sandbox execution
linuxRun swftools in a container or sandbox with minimal privileges
# Example using Docker with read-only filesystem
docker run --read-only -v /input:/input:ro swftools
🧯 If You Can't Patch
- Implement strict input validation for SWF files before processing
- Run swftools with minimal privileges (non-root user) in isolated environments
🔍 How to Verify
Check if Vulnerable:
Check swftools version: swftools --version. If version is 20200710 or earlier, system is vulnerable.Check Version:
swftools --versionVerify Fix Applied:
Verify updated version: swftools --version should show version newer than 20200710. Test with known safe SWF files to ensure functionality.📡 Detection & Monitoring
Log Indicators:
- Segmentation faults or abnormal termination of swftools processes
- Unexpected memory allocation patterns in system logs
Network Indicators:
- Unusual outbound connections from swftools processes
- Large SWF file uploads to systems using swftools
SIEM Query:
process_name:"swftools" AND (event_type:"crash" OR exit_code:139)