auditing-webauthn-and-passkey-flows SKILL.md skillA
auditing-webauthn-and-passkey-flows 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/auditing-webauthn-and-passkey-flows@git:20260821.57dfaf1Pins git:20260821.57dfaf1 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/auditing-webauthn-and-passkey-flows/SKILL.md- Versions recorded
- 1
- Latest version
- git:20260821.57dfaf1, committed Aug 21, 2026
- Size
- 10,034 bytes
- Repository stars
- 26
- License
- MIT
Audit the server side of passwordless authentication for ceremony-verification bugs that let an attacker-shaped response become an authenticated session. Covers a registration or authentication ceremony whose challenge is not bound to a server-issued single-use value, an origin or relying-party identifier that is never checked or checked by substring, a user-verification flag ignored when policy required it, attestation accepted when it was required, a signature counter regression that hides a…
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
# Auditing passkey and WebAuthn ceremonies: when a verified signature seats the wrong user A passkey ceremony proves that some authenticator signed a challenge. It does not, by itself, prove who is signing in. Every WebAuthn bug worth finding lives in the gap between "this signature is valid" and "therefore user U is logged in," and that gap is closed only by a specific list of server-side checks. When one of those checks is missing, homegrown, or bypassable, attacker-shaped bytes from the ceremony response flow straight into an authenticated session. You find these by reading the verification path and asking, for each required check, whether it runs and whether the value it checks is the one the attacker cannot forge. ## When to use - Code verifies a WebAuthn registration or authentication response and then creates a credential or a session. - The application implements the ceremony itself, or calls a library but supplies the policy and expected values. - You want to know whether a valid signature can be replayed, phished, or bound to the wrong account. ## Scope check Test passkey flows only on systems you own or are authorized to assess, with test accounts and test …
Read the whole file at its exact version.
How to install
mdr add unboundcompute/security-agent-skills/auditing-webauthn-and-passkey-flows@sha256:2ffc7910341c2723The line at the top of this page pins the label git:20260821.57dfaf1, 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_b2oq2se74totstu6)
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Versions
The registry has recorded 1 version of this file, committed on Aug 21, 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 (10034 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_b2oq2se74totstu6 GET https://markdownregistry.com/api/v1/resolve?ref=unboundcompute/security-agent-skills/auditing-webauthn-and-passkey-flows GET https://markdownregistry.com/api/v1/blob/2ffc7910341c27235f58b8c72e23dfe8c0de1c81052aaf64476bca6901cbee54
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.