CVE-2021-45909
📋 TL;DR
CVE-2021-45909 is a heap-based buffer overflow vulnerability in gif2apng's DecodeLZW function that allows attackers to write arbitrary data beyond buffer boundaries. This affects systems running gif2apng 1.9 for converting GIF images to APNG format. Attackers could potentially execute arbitrary code or crash the application.
💻 Affected Systems
- gif2apng
📦 What is this software?
Gif2apng by Gif2apng Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or installation of persistent malware.
Likely Case
Application crash (denial of service) or limited memory corruption leading to unstable behavior.
If Mitigated
Application crash with no further impact if proper memory protections and sandboxing are in place.
🎯 Exploit Status
Exploitation requires crafting a malicious GIF file that triggers the buffer overflow during LZW decoding.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 1.9-1 (Debian patched version)
Vendor Advisory: https://lists.debian.org/debian-lts-announce/2022/03/msg00008.html
Restart Required: No
Instructions:
1. Update package via system package manager: 'sudo apt update && sudo apt upgrade gif2apng' 2. Verify installation of patched version 1.9-1 or later.
🔧 Temporary Workarounds
Disable gif2apng processing
linuxRemove or disable gif2apng from systems where it's not essential
sudo apt remove gif2apng
Restrict file processing
allImplement input validation to reject suspicious GIF files before processing
🧯 If You Can't Patch
- Implement strict input validation for GIF files before passing to gif2apng
- Run gif2apng in a sandboxed environment with limited privileges
🔍 How to Verify
Check if Vulnerable:
Check gif2apng version: 'gif2apng --version' or 'dpkg -l | grep gif2apng'Check Version:
gif2apng --version 2>/dev/null || dpkg -l gif2apng 2>/dev/null || rpm -q gif2apng 2>/dev/nullVerify Fix Applied:
Verify version is 1.9-1 or later: 'dpkg -l gif2apng | grep ^ii' should show 1.9-1📡 Detection & Monitoring
Log Indicators:
- Segmentation fault crashes of gif2apng
- Memory access violation errors
- Abnormal process termination
Network Indicators:
- Uploads of GIF files followed by application crashes
- Unusual outbound connections after GIF processing
SIEM Query:
process_name:"gif2apng" AND (event_type:"crash" OR exit_code:139)