CVE-2020-36120
📋 TL;DR
A buffer overflow vulnerability in Libsixel's sixel_encoder_encode_bytes function allows attackers to cause denial of service by sending specially crafted input. This affects applications that use Libsixel v1.8.6 for sixel graphics encoding. Systems processing untrusted sixel data are at risk.
💻 Affected Systems
- Libsixel
📦 What is this software?
Libsixel by Libsixel Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise if the buffer overflow can be leveraged for arbitrary code execution.
Likely Case
Application crash causing denial of service, potentially disrupting services that rely on sixel graphics processing.
If Mitigated
Limited impact with proper input validation and memory protections, potentially just application instability.
🎯 Exploit Status
Buffer overflow vulnerabilities in widely used libraries often see rapid exploitation development.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v1.8.7 and later
Vendor Advisory: https://github.com/saitoha/libsixel/issues/143
Restart Required: Yes
Instructions:
1. Check current Libsixel version
2. Update to v1.8.7 or later via package manager or source
3. Rebuild applications using Libsixel
4. Restart affected services
🔧 Temporary Workarounds
Input Validation
allImplement strict input validation for sixel data before passing to Libsixel functions
Memory Protection
linuxEnable ASLR and other memory protection mechanisms to reduce exploit success
sysctl -w kernel.randomize_va_space=2
🧯 If You Can't Patch
- Isolate systems using Libsixel behind firewalls with strict input filtering
- Implement application-level input validation and size limits for sixel data
🔍 How to Verify
Check if Vulnerable:
Check if Libsixel v1.8.6 is installed and used by applicationsCheck Version:
libsixel-config --version || dpkg -l | grep libsixel || rpm -qa | grep libsixelVerify Fix Applied:
Verify Libsixel version is v1.8.7 or later and applications have been rebuilt📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults
- Memory access violation errors in logs
- Unusual sixel processing activity
Network Indicators:
- Large or malformed sixel data streams
- Repeated connection attempts to sixel-enabled services
SIEM Query:
source="application.logs" AND ("segmentation fault" OR "buffer overflow" OR "sixel")