CVE-2021-40633
📋 TL;DR
CVE-2021-40633 is a memory leak vulnerability in gif2rgb, a utility in giflib 5.1.4, allowing remote attackers to cause denial of service by triggering an out-of-memory exception via a malicious GIF file. This affects systems using giflib for GIF image processing, particularly those that handle untrusted GIF files.
💻 Affected Systems
- giflib
📦 What is this software?
Giflib by Giflib Project
⚠️ Risk & Real-World Impact
Worst Case
Complete system crash or service disruption due to memory exhaustion, potentially leading to downtime for applications relying on giflib.
Likely Case
Denial of service in applications processing GIF files, causing temporary unavailability or performance degradation.
If Mitigated
Minimal impact if patched or if input validation restricts untrusted GIF files.
🎯 Exploit Status
Exploitation involves providing a crafted GIF file; no authentication is required if the vulnerable utility is accessible.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: giflib 5.1.5 or later
Vendor Advisory: https://sourceforge.net/p/giflib/bugs/157/
Restart Required: No
Instructions:
1. Download the latest giflib version from the official repository. 2. Compile and install the updated version. 3. Replace any vulnerable binaries with the patched ones.
🔧 Temporary Workarounds
Disable or restrict gif2rgb usage
linuxRemove or limit access to the gif2rgb utility to prevent processing of untrusted GIF files.
sudo rm /usr/bin/gif2rgb
sudo chmod 000 /usr/bin/gif2rgb
🧯 If You Can't Patch
- Implement strict input validation to reject or sanitize GIF files from untrusted sources.
- Monitor system memory usage and set limits on processes using giflib to mitigate denial of service.
🔍 How to Verify
Check if Vulnerable:
Check the giflib version installed; if it is 5.1.4, the system is vulnerable.Check Version:
gif2rgb --version 2>&1 | grep -i version || dpkg -l | grep giflib || rpm -qa | grep giflibVerify Fix Applied:
Verify that the giflib version is 5.1.5 or later after patching.📡 Detection & Monitoring
Log Indicators:
- Log entries indicating out-of-memory errors or crashes in processes using gif2rgb.
Network Indicators:
- Unusual uploads or transfers of GIF files to systems running giflib.
SIEM Query:
Example: search for 'out of memory' OR 'segmentation fault' in logs related to gif2rgb processes.