hunting-host-header-and-url-parsing-trust SKILL.md skillA
hunting-host-header-and-url-parsing-trust from unboundcompute/security-agent-skills is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add unboundcompute/security-agent-skills/hunting-host-header-and-url-parsing-trust@git:20260903.6dac719Pins git:20260903.6dac719 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- unboundcompute/security-agent-skills
- Path
skills/hunting-host-header-and-url-parsing-trust/SKILL.md- Versions recorded
- 1
- Latest version
- git:20260903.6dac719, committed Sep 3, 2026
- Size
- 10,585 bytes
- Repository stars
- 26
- License
- MIT
Hunt trust placed in the Host or a forwarded host header and in inconsistently parsed URLs, where the app builds absolute links, keys a cache, routes a request, or matches an allowlist from a header or a parsed URL an attacker can influence or that two components parse differently. Use when a service derives its own external URL from the request, when a cache or router keys on the host, or when a security decision parses a URL. Covers password-reset and verification-link poisoning, cache…
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
# Hunting host header and URL parsing trust: when the app believes the request about its own name An application often needs to know its own address, to put a link in an email or to decide where a request belongs. The easy way is to read it from the incoming request: the Host header, or a forwarded-host header a proxy added. But those are attacker-controlled, and a server that builds a password-reset link from the Host sends the victim a link pointing at the attacker's domain. A shared cache that keys on a header the origin reflects serves the poisoned response to everyone. A router that trusts a forwarded host reaches an internal virtual host. The related trap is URL parsing: when the component that checks a URL and the component that uses it disagree about where the host ends, an allowlist passes a URL that resolves somewhere else. The bug is trusting the request's account of the host, or one parser's reading of a URL, as if it were authoritative. You find it by tracing where self-URLs, cache keys, routes, and allowlists get their host. ## When to use - The app builds absolute URLs (reset, verification, invite links) from the request's Host or forwarded host. …
Read the whole file at its exact version.
How to install
mdr add unboundcompute/security-agent-skills/hunting-host-header-and-url-parsing-trust@sha256:b46af7f9063cdc0bThe line at the top of this page pins the label git:20260903.6dac719, 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_ltmifren7hiuzxt2)
2 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 1 version of this file, committed on Sep 3, 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 (10585 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
unboundcompute/security-agent-skills · 26 stars · license MIT · pushed 2026-09-08 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_ltmifren7hiuzxt2 GET https://markdownregistry.com/api/v1/resolve?ref=unboundcompute/security-agent-skills/hunting-host-header-and-url-parsing-trust GET https://markdownregistry.com/api/v1/blob/b46af7f9063cdc0b7a8b3aac9fc6a02be1c0fb8239d0b438b8ae441b22c8fa5d
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.