CVE-2023-49552
📋 TL;DR
CVE-2023-49552 is an out-of-bounds write vulnerability in Cesanta mjs 2.20.0's mjs_op_json_stringify function that allows remote attackers to cause denial of service. This affects any application using the vulnerable mjs library version. Attackers can trigger crashes or potentially execute arbitrary code by exploiting this memory corruption issue.
💻 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
Likely Case
Denial of service causing application crashes and service disruption
If Mitigated
Application crash with limited impact if properly sandboxed
🎯 Exploit Status
Proof of concept available in GitHub issue #256, demonstrates crash via crafted input
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.21.0 or later
Vendor Advisory: https://github.com/cesanta/mjs/issues/256
Restart Required: Yes
Instructions:
1. Update mjs to version 2.21.0 or later. 2. Rebuild any applications using mjs. 3. Restart affected services.
🔧 Temporary Workarounds
Disable JSON stringify functionality
allRemove or disable mjs_op_json_stringify function usage if not required
Modify source code to avoid mjs_op_json_stringify calls
Input validation and sanitization
allImplement strict input validation for JSON operations
Add bounds checking before mjs_op_json_stringify calls
🧯 If You Can't Patch
- Network segmentation to isolate vulnerable systems
- Implement WAF rules to block malicious JSON payloads
🔍 How to Verify
Check if Vulnerable:
Check if mjs version is 2.20.0 in application dependenciesCheck Version:
Check package manifest or run: grep -r "mjs" package.jsonVerify Fix Applied:
Verify mjs version is 2.21.0 or later after update📡 Detection & Monitoring
Log Indicators:
- Application crashes
- Segmentation faults
- Memory corruption errors
Network Indicators:
- Unusual JSON payloads to mjs endpoints
- Repeated crash-inducing requests
SIEM Query:
source="application.log" AND ("segmentation fault" OR "mjs" OR "json_stringify")