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HTTP Request Smuggling is a technique where an attacker manipulates the way a web server processes sequences of HTTP requests, leading to security breaches such as cache poisoning, session hijacking, or unauthorized access.
How HTTP Request Smuggling Works
The attack exploits discrepancies in how front-end (proxy) and back-end servers interpret HTTP requests. By crafting a malicious request, an attacker can “smuggle” a second request that gets processed unexpectedly.
Example Attack Scenario
1. Initial Request (Legitimate)
GET /societal-impact/ HTTP/1.1 Host: ai.example.com Connection: keep-alive
2. Malicious Smuggled Request
GET / HTTP/1.1 Host: attacker.com
If the front-end server processes `Connection: keep-alive` but the back-end doesn’t, the smuggled request (GET /) may execute, revealing sensitive data.
You Should Know: Practical Exploitation & Defense
Step-by-Step Exploitation (Using Burp Suite)
1. Capture a Legitimate Request
- Intercept a request in Burp Suite (e.g.,
GET /example HTTP/1.1). - Remove `Connection: close` to force keep-alive.
2. Craft a Smuggled Request
POST /vulnerable-endpoint HTTP/1.1 Host: target.com Transfer-Encoding: chunked 0 GET /admin HTTP/1.1 Host: attacker-controlled.com
3. Modify Burp Settings
- Disable “Update Content-Length” in Burp Repeater.
- Enable “Allow HTTP/1.0” to bypass security checks.
4. Send the Request
- If successful, the server processes `GET /admin` separately, potentially exposing admin panels.
Defensive Measures
- Server Configuration:
- Reject ambiguous requests (mixed `Content-Length` &
Transfer-Encoding). - Use HTTP/2 (enforces stricter parsing).
- WAF Rules:
- Block requests with duplicate headers.
- Code-Level Fixes:
- Normalize incoming requests before processing.
Relevant Linux & Windows Commands
- Check HTTP Headers (Linux):
curl -v http://example.com -H "Connection: keep-alive"
- Test for Smuggling (Windows PowerShell):
Invoke-WebRequest -Uri "http://example.com" -Headers @{"Connection"="keep-alive"} - Log Analysis (Linux):
grep "HTTP/1.1 200" /var/log/nginx/access.log
What Undercode Say
HTTP Request Smuggling remains a high-risk vulnerability due to inconsistent server implementations. Organizations must enforce strict header validation and monitor for anomalous requests. Attackers increasingly abuse this in cloud environments, making proactive defense critical.
Expected Output:
A successful smuggling attack returns two responses:
- The expected `200 OK` for the first request.
- A second `200 OK` (or
403 Forbidden) for the smuggled request, indicating vulnerability.
Prediction
As APIs and microservices grow, request smuggling attacks will escalate, targeting cloud-native apps. Automated tools will emerge to exploit weak parsing logic in serverless architectures.
Reference:
IT/Security Reporter URL:
Reported By: Activity 7335384329209999371 – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
