request-smuggling

HTTP request smuggling and desync technique list, including the 2025-26 "HTTP/1.1 must die" desync-endgame classes (0.CL, CL.0, H2.TE, TE.TE chunk extensions, response queue poisoning, dangling-byte, browser-powered desyncs). Converted from master-pentest-prompt.md Phase 4. Use when a target sits behind a reverse proxy/CDN/load balancer and front-end/back-end parsing discrepancies are worth probing.

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Repository: ankitsingh015/HuntMCP
Last source activity: August 24, 2026 at 11:04
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HTTP request smuggling / desync

When to use

Any target behind a reverse proxy, CDN, or load balancer -- the entire category depends on a front-end/back-end parser discrepancy existing, which is common in exactly that architecture. Worth a dedicated pass whenever httpx-mcp's recon shows a CDN/proxy signature (CF-RAY, X-Served-By, etc.).

Core techniques

CL.TE, TE.CL, TE.TE, H2.CL, H2.TE downgrade smuggling.

Front-end/back-end parser discrepancy detection.

Client-side desync (CSD) -- browser-level poisoning.

Response queue poisoning (steal victim responses).

CRLF in HTTP/2 header values (request splitting, CVE-2025-57804-class).

Chained: smuggling -> cache poisoning -> stored XSS served to all users.

Tools: Burp HTTP Request Smuggler v3.0 (Kettle), Turbo Intruder, Param Miner.

2025-26 desync-endgame classes (Kettle, "HTTP/1.1 must die")

0.CL desync: a request with zero body before Content-Length, plus the obfuscated Expect variant.

CL.0 (Content-Length without Transfer-Encoding) via Expect header, HEAD gadget, or 403-triggered CL.0.

V-H discrepancy: verify hops, defer to Host; H-V: trust Host, verify.

H2.TE (HTTP/2 -> HTTP/1.1 Transfer-Encoding conversion) and TE.0 dechunking.

TE.TE chunk extensions (obfuscating transfer-encoding).

Exotic desync triggers: Transfer-Encoding: gzip, multipart/byteranges, Range: ,, (comma), Expect:\t100-continue, Upgrade: websocket, CONNECT, Max-Forwards: 0, Early-data: 1 (TLS 1.3 early-data smuggling).

Response Queue Poisoning (RQP): poison the shared HTTP/1.1 queue.

Dangling-byte technique: a single trailing byte, race-free, fully reliable.

CRLF-powered desync: behead HTTP streams, desync worms (browser-compatible, self-replicating, no server cooperation needed), request splitting.

Browser-powered desyncs (fetch-compatible), connection-locked and IP-locked desyncs (use same-IP hosts to beat locking).

HTTP request tunnelling: blind desync into back-end tunnels.

Range Cache Poisoning + HEAD gadget: poison the cache of HEAD-only resources.

Automated discovery: HTTP Request Smuggler v3.0 / HTTP Terminator (Kettle/PortSwigger) for novel-class discovery on any target.

Working order

Start with single-request variants (no race needed), then move to RQP (targeted: send one queued victim request, observe queue replay).