CVE-2020-25756
📋 TL;DR
A buffer overflow vulnerability in Cesanta Mongoose's mg_get_http_header function allows remote attackers to execute arbitrary code or cause denial of service by sending specially crafted HTTP headers. This affects all applications using vulnerable versions of the Mongoose embedded web server library. The vulnerability is particularly dangerous for internet-facing services.
💻 Affected Systems
- Cesanta Mongoose embedded web server/library
📦 What is this software?
Mongoose by Cesanta
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Denial of service causing application crashes and service disruption.
If Mitigated
Limited impact if proper input validation and memory protection mechanisms are in place.
🎯 Exploit Status
Exploitation requires crafting specific HTTP headers but no authentication is needed. The committer's note suggests practical exploitation may be difficult.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 6.18
Vendor Advisory: https://github.com/cesanta/mongoose/issues/1135
Restart Required: Yes
Instructions:
1. Update Mongoose library to version after 6.18. 2. Recompile and redeploy affected applications. 3. Restart services using the updated library.
🔧 Temporary Workarounds
Input validation filter
allImplement custom HTTP header validation to reject malformed headers
Implement custom request handler to validate header lengths before processing
Memory protection
linuxEnable ASLR and DEP/stack protection on systems
sudo sysctl -w kernel.randomize_va_space=2
Check compiler flags for -fstack-protector-all
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block malformed HTTP headers
- Network segmentation to isolate vulnerable systems from untrusted networks
🔍 How to Verify
Check if Vulnerable:
Check application dependencies for Mongoose version <= 6.18Check Version:
Check application build configuration or grep for MONGOOSE_VERSION in source codeVerify Fix Applied:
Verify Mongoose version > 6.18 is installed and application functions normally📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP header patterns
- Application crashes/segfaults
- Abnormally long header values
Network Indicators:
- HTTP requests with unusually long or malformed headers
- Multiple connection attempts with varying headers
SIEM Query:
source="web_logs" AND (header_length>8192 OR header_name CONTAINS ".." OR header_value CONTAINS shell_patterns)