h2c-websocket-smuggling SKILL.md skillA
h2c-websocket-smuggling from dreadnode/capabilities is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add dreadnode/capabilities/h2c-websocket-smuggling@git:20260518.7b5f854Pins git:20260518.7b5f854 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- dreadnode/capabilities
- Path
capabilities/web-security/skills/h2c-websocket-smuggling/SKILL.md- Versions recorded
- 1
- Latest version
- git:20260518.7b5f854, committed May 18, 2026
- Size
- 4,119 bytes
- Repository stars
- 22
- License
- MIT
Bypass reverse proxy ACLs via H2C upgrade or WebSocket tunnel. Use when proxy blocks internal paths but forwards Upgrade headers, or when standard CL.TE/TE.CL smuggling fails.
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
# H2C & WebSocket Smuggling Proxy sees `Upgrade: h2c` or `Upgrade: websocket`, establishes persistent tunnel, stops inspecting individual requests. You now talk directly to the backend, bypassing path-based ACLs, WAF rules, and auth checks enforced at the proxy layer. ## When This Beats Standard Smuggling - CL.TE/TE.CL/TE.0 all fail (proxy and backend agree on body parsing) - Proxy enforces path ACLs (`/admin` blocked) but forwards upgrade headers - Target has WebSocket endpoints (even broken ones) ## H2C Smuggling ### Required Headers (all three) ```http GET / HTTP/1.1 Host: target.com Upgrade: h2c HTTP2-Settings: AAMAAABkAARAAAAAAAIAAAAA Connection: Upgrade, HTTP2-Settings ``` ### Proxy Vulnerability Matrix **Inherently vulnerable** (forward upgrade headers by default): - HAProxy, Traefik, Nuster **Vulnerable if misconfigured** (forward when `proxy_pass` or backend config allows): - AWS ALB/CLB, nginx, Apache, Squid, Varnish, Kong, Envoy, Apache Traffic Server ### Key Insight …
Read the whole file at its exact version.
How to install
mdr add dreadnode/capabilities/h2c-websocket-smuggling@sha256:e8fe2bb9301884e2The line at the top of this page pins the label git:20260518.7b5f854, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
[](https://markdownregistry.com/a/art_extm3fjm5z5w2d7n)
3 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 1 version of this file, committed on May 18, 2026.
Audit of the latest version
- pass: Frontmatter block present
- pass: Frontmatter declares a name
- pass: Frontmatter declares a description
- pass: Size between 200 bytes and 200 KB (4119 bytes)
- pass: No zero-width or bidi control characters
- pass: No instruction hidden inside an HTML comment
- pass: No link to an exfiltration or paste host
- pass: No credential-shaped string
- pass: No instruction to send local credentials anywhere
- pass: No text hidden with inline styles
- pass: No prompt-injection phrasing
- pass: No curl or wget piped into a shell
- pass: No recursive delete of root, home or parent
- pass: No instruction to read or print local credentials
- pass: No base64 blob over 200 characters
- pass: No link to a raw IP address
- pass: No script tag
Source
dreadnode/capabilities · 22 stars · license MIT · pushed 2026-11-02 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_extm3fjm5z5w2d7n GET https://markdownregistry.com/api/v1/resolve?ref=dreadnode/capabilities/h2c-websocket-smuggling GET https://markdownregistry.com/api/v1/blob/e8fe2bb9301884e28d442b42b91b0918d8564a3b92a6b62986a493daa513c3dd
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.