CVE-2021-45907
📋 TL;DR
CVE-2021-45907 is a stack-based buffer overflow vulnerability in gif2apng 1.9 that occurs during GIF to APNG conversion. While attackers have limited control over the data written to the stack, making control flow hijacking unlikely, the vulnerability could still lead to crashes or denial of service. Users and systems running gif2apng 1.9 for image conversion are affected.
💻 Affected Systems
- gif2apng
📦 What is this software?
Gif2apng by Gif2apng Project
⚠️ Risk & Real-World Impact
Worst Case
Application crash leading to denial of service; potential for arbitrary code execution if attackers can influence the overflow data (though described as unlikely).
Likely Case
Application crash or unexpected termination during GIF to APNG conversion, causing service disruption.
If Mitigated
Minimal impact with proper input validation and memory protections enabled (ASLR, stack canaries).
🎯 Exploit Status
The vulnerability description indicates attackers have little influence over the data written, making control flow subversion unlikely.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 1.10 or later
Vendor Advisory: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1002669
Restart Required: No
Instructions:
1. Check current version: gif2apng --version
2. Update via package manager: sudo apt update && sudo apt upgrade gif2apng
3. Verify update: gif2apng --version should show 1.10 or higher
🔧 Temporary Workarounds
Disable gif2apng processing
linuxRemove or disable gif2apng from automated processing pipelines
sudo apt remove gif2apng
sudo mv /usr/bin/gif2apng /usr/bin/gif2apng.disabled
Input validation wrapper
linuxCreate a wrapper script that validates GIF files before passing to gif2apng
#!/bin/bash
# Validate file is actually a GIF before processing
if file "$1" | grep -q "GIF"; then
/usr/bin/gif2apng "$@"
else
echo "Invalid file type"
exit 1
fi
🧯 If You Can't Patch
- Implement strict input validation - only allow trusted, verified GIF files to be processed by gif2apng
- Run gif2apng in a sandboxed environment with limited privileges and memory restrictions
🔍 How to Verify
Check if Vulnerable:
Run: gif2apng --version | grep -q '1.9' && echo 'VULNERABLE' || echo 'NOT VULNERABLE'Check Version:
gif2apng --versionVerify Fix Applied:
Run: gif2apng --version | grep -q '1.1[0-9]' && echo 'PATCHED' || echo 'STILL VULNERABLE'📡 Detection & Monitoring
Log Indicators:
- Segmentation fault or crash logs from gif2apng process
- Unexpected termination of gif2apng conversion jobs
Network Indicators:
- N/A - local file processing vulnerability
SIEM Query:
process.name:"gif2apng" AND (event.action:"segmentation_fault" OR event.action:"crash")