CVE-2023-27730
📋 TL;DR
CVE-2023-27730 is a memory corruption vulnerability in Nginx NJS JavaScript engine that can cause segmentation faults via the njs_lvlhsh_find function. This affects systems running Nginx with NJS module enabled, potentially leading to denial of service or arbitrary code execution. The vulnerability is present in NJS version 0.7.10 and earlier.
💻 Affected Systems
- Nginx NJS (JavaScript engine for Nginx)
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise if the segmentation violation can be weaponized to execute arbitrary code.
Likely Case
Denial of service through Nginx worker crashes, causing service disruption and potential availability issues.
If Mitigated
Limited impact with proper segmentation and privilege separation, potentially only affecting individual worker processes.
🎯 Exploit Status
The GitHub issue includes technical details and proof-of-concept information. Exploitation requires triggering the vulnerable function through NJS JavaScript execution.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: NJS version 0.7.11 and later
Vendor Advisory: https://github.com/nginx/njs/issues/615
Restart Required: Yes
Instructions:
1. Update NJS to version 0.7.11 or later. 2. Recompile Nginx with updated NJS module if using source build. 3. Restart Nginx service to apply changes.
🔧 Temporary Workarounds
Disable NJS Module
allRemove or disable NJS module configuration in Nginx if not required
# Remove njs module from nginx configuration
# Comment out or remove 'load_module modules/ngx_http_js_module.so;' from nginx.conf
# Remove any js_* directives from server/location blocks
Restrict NJS Usage
allLimit NJS execution to trusted contexts only
# In nginx.conf, restrict js_content/js_set directives to specific locations
location /trusted {
js_content handler;
}
# Add authentication/authorization before NJS execution
🧯 If You Can't Patch
- Implement strict network segmentation to isolate vulnerable Nginx instances
- Deploy web application firewall (WAF) rules to detect and block suspicious NJS-related requests
🔍 How to Verify
Check if Vulnerable:
Check NJS version: njs -v or examine nginx configuration for NJS module loading and versionCheck Version:
njs -v 2>/dev/null || grep -i njs /path/to/nginx/conf/nginx.confVerify Fix Applied:
Verify NJS version is 0.7.11 or later: njs -v should show version >= 0.7.11📡 Detection & Monitoring
Log Indicators:
- Segmentation fault errors in Nginx error logs
- Worker process crashes with signal 11 (SIGSEGV)
- Repeated NJS-related errors
Network Indicators:
- Unusual patterns of requests to NJS-enabled endpoints
- Requests containing malformed JavaScript or unusual parameters
SIEM Query:
source="nginx-error.log" AND ("segmentation fault" OR "signal 11" OR "SIGSEGV")