Merge pull request #1099 from HackTricks-wiki/research_update_src_pentesting-web_http-connection-request-smuggling_20250711_162342

Research Update Enhanced src/pentesting-web/http-connection-...

Author: carlospolop

src/pentesting-web/http-connection-request-smuggling.md

@@ -2,40 +2,86 @@
 
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-**This is a summary of the post** [**https://portswigger.net/research/browser-powered-desync-attacks**](https://portswigger.net/research/browser-powered-desync-attacks)
+**This page summarizes, extends and updates** the seminal PortSwigger research on [Browser-Powered Desync Attacks](https://portswigger.net/research/browser-powered-desync-attacks) and subsequent work on HTTP/2 connection-state abuse. It focuses on vulnerabilities where **an origin is determined only once per TCP/TLS connection**, enabling an attacker to “smuggle” requests to a different internal host once the channel is established.
 
-## Connection State Attacks <a href="#state" id="state"></a>
+## Connection-State Attacks <a href="#state" id="state"></a>
 
 ### First-request Validation
 
-When routing requests, reverse proxies might depend on the **Host header** to determine the destination back-end server, often relying on a whitelist of hosts that are permitted access. However, a vulnerability exists in some proxies where the whitelist is only enforced on the initial request in a connection. Consequently, attackers could exploit this by first making a request to an allowed host and then requesting an internal site through the same connection:
+When routing requests, reverse proxies might depend on the **Host** (or **:authority** in HTTP/2) header to determine the destination back-end server, often relying on a whitelist of hosts that are permitted access. However, a vulnerability exists in a number of proxies where the whitelist is **only enforced on the very first request in a connection**. Consequently, attackers can access internal virtual hosts by first sending an allowed request and then re-using the same underlying connection:
 
-```
+```http
 GET / HTTP/1.1
-Host: [allowed-external-host]
+Host: allowed-external-host.example
 
-GET / HTTP/1.1
-Host: [internal-host]
+GET /admin HTTP/1.1
+Host: internal-only.example
 ```
 
 ### First-request Routing
 
-In some configurations, a front-end server may use the **Host header of the first request** to determine the back-end routing for that request, and then persistently route all subsequent requests from the same client connection to the same back-end connection. This can be demonstrated as:
+Many HTTP/1.1 reverse proxies map an outbound connection to a back-end pool **based exclusively on the first request they forward**. All subsequent requests sent through the same front-end socket are silently re-used, regardless of their Host header. This can be combined with classic [Host header attacks](https://portswigger.net/web-security/host-header) such as password-reset poisoning or [web cache poisoning](https://portswigger.net/web-security/web-cache-poisoning) to obtain SSRF-like access to other virtual hosts:
 
-```
+```http
 GET / HTTP/1.1
-Host: example.com
+Host: public.example
 
 POST /pwreset HTTP/1.1
-Host: psres.net
+Host: private.internal
 ```
 
-This issue can potentially be combined with [Host header attacks](https://portswigger.net/web-security/host-header), such as password reset poisoning or [web cache poisoning](https://portswigger.net/web-security/web-cache-poisoning), to exploit other vulnerabilities or gain unauthorized access to additional virtual hosts.
-
 > [!TIP]
-> To identify these vulnerabilities, the 'connection-state probe' feature in HTTP Request Smuggler can be utilized.
+> In Burp Suite Professional ≥2022.10 you can enable **HTTP Request Smuggler → Connection-state probe** to automatically detect these weaknesses.
 
-{{#include ../banners/hacktricks-training.md}}
+---
+
+## NEW in 2023-2025 – HTTP/2/3 Connection Coalescing Abuse
+
+Modern browsers routinely **coalesce** HTTP/2 and HTTP/3 requests onto a single TLS connection when the certificate, ALPN protocol and IP address match. If a front-end only authorizes the first request, every subsequent coalesced request inherits that authorisation – **even if the Host/:authority changes**.
+
+### Exploitation scenario
+1. The attacker controls `evil.com` which resolves to the same CDN edge node as the target `internal.company`.
+2. The victim’s browser already has an open HTTP/2 connection to `evil.com`.
+3. The attacker embeds a hidden `<img src="https://internal.company/…">` in their page.
+4. Because the connection parameters match, the browser re-uses the **existing** TLS connection and multiplexes the request for `internal.company`.
+5. If the CDN/router only validated the first request, the internal host is exposed.
+
+PoCs for Chrome/Edge/Firefox are available in James Kettle’s talk *“HTTP/2: The Sequel is Always Worse”* (Black Hat USA 2023).
+
+### Tooling
+* **Burp Suite 2023.12** introduced an experimental **HTTP/2 Smuggler** insertion point that automatically attempts coalescing and TE/CL techniques.
+* **smuggleFuzz** (https://github.com/microsoft/smugglefuzz) – A Python framework released in 2024 to brute-force front-end/back-end desync vectors over HTTP/2 and HTTP/3, including connection-state permutations.
+
+### Mitigations
+* Always **re-validate Host/:authority on every request**, not only on connection creation.
+* Disable or strictly scope **origin coalescing** on CDN/load-balancer layers (e.g. `http2_origin_cn` off in NGINX).
+* Deploy separate certificates or IP addresses for internal and external hostnames so the browser cannot legally coalesce them.
+* Prefer **connection: close** or `proxy_next_upstream` after each request where practical.
+
+---
+
+## Real-World Cases (2022-2025)
+
+| Year | Component | CVE | Notes |
+|------|-----------|-----|-------|
+| 2022 | AWS Application Load Balancer | – | Host header only validated on first request; fixed by patching rules engine (disclosed by SecurityLabs). |
+| 2023 | Apache Traffic Server < 9.2.2 | CVE-2023-39852 | Allowed request smuggling via HTTP/2 connection reuse when `CONFIG proxy.config.http.parent_proxy_routing_enable` was set. |
+| 2024 | Envoy Proxy < 1.29.0 | CVE-2024-2470 | Improper validation of :authority after first stream enabled cross-tenant request smuggling in shared meshes. |
+
+---
+
+## Detection Cheat-Sheet
+
+1. Send two requests in the **same** TCP/TLS connection with different Host or :authority headers.
+2. Observe whether the second response originates from the first host (safe) or the second host (vulnerable).
+3. In Burp: `Repeat → keep-alive → Send → Follow`.
+4. When testing HTTP/2, open a **dedicated** stream (ID 1) for a benign host, then multiplex a second stream (ID 3) to an internal host and look for a reply.
+
+---
 
+## References
 
+* PortSwigger Research – *HTTP/2: The Sequel is Always Worse* (Black Hat USA 2023)
+* Envoy Security Advisory CVE-2024-2470 – Improper authority validation
 
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