CVE-2021-46509
📋 TL;DR
CVE-2021-46509 is a stack overflow vulnerability in Cesanta MJS v2.20.0's JSON parsing functionality that allows attackers to execute arbitrary code or cause denial of service. This affects any application using the vulnerable MJS library version. Attackers can exploit this by providing specially crafted JSON input to trigger the overflow.
💻 Affected Systems
- Cesanta MJS
📦 What is this software?
Mjs 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 with proper input validation and memory protection mechanisms in place.
🎯 Exploit Status
The vulnerability is in a core JSON parsing function and requires minimal attacker skill to exploit.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v2.20.1 or later
Vendor Advisory: https://github.com/cesanta/mjs/issues/200
Restart Required: Yes
Instructions:
1. Update MJS to version 2.20.1 or later. 2. Recompile applications using the updated library. 3. Restart affected services.
🔧 Temporary Workarounds
Disable JSON parsing
allRemove or disable JSON parsing functionality if not required
Recompile MJS with JSON support disabled
Input validation
allImplement strict input validation for JSON data
🧯 If You Can't Patch
- Implement strict input validation and sanitization for all JSON inputs
- Deploy memory protection mechanisms like ASLR and stack canaries
🔍 How to Verify
Check if Vulnerable:
Check if MJS version is 2.20.0 in application dependencies or library filesCheck Version:
grep -r "MJS_VERSION" /path/to/mjs/headers/ || check package manager for mjs versionVerify Fix Applied:
Verify MJS version is 2.20.1 or later and test JSON parsing with various inputs📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults
- Unusual memory usage patterns
- Multiple failed JSON parsing attempts
Network Indicators:
- Large or malformed JSON payloads to application endpoints
SIEM Query:
source="application.logs" AND ("segmentation fault" OR "stack overflow" OR "mjs")