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saml-sso-assertion-attacks — Claude Code skill: testing SAML

A playbook for SAML SSO testing: which XML nodes are signed, how Audience and ACS checks behave, and where IdP/SP trust breaks down.

Install into Claude Code · Skills CLI (Vercel) All methods and platforms ↓ 
npx skills add yaklang/hack-skills --skill saml-sso-assertion-attacks -a claude-code
Open on GitHub

What saml-sso-assertion-attacks does

The skill loads when a target signs users in through SAML: you see SAMLRequest, SAMLResponse, XML assertions or ACS endpoints, and the flow goes through an external IdP with browser POST or redirect binding.

Inside is a table of checks grouped by theme: signature validation (unsigned assertion accepted, wrong node signed, signature wrapping), weak Audience, Recipient, Destination or ACS validation, issuer trust and multi-tenant confusion, replay and freshness (InResponseTo, NotBefore, NotOnOrAfter), account mapping by email and case folding, and XML parser behaviour. A four-step triage follows: capture one full login round trip, inspect which nodes are signed and which attributes drive account binding, compare SP-initiated against IdP-initiated flows, then test replay and assertion placement confusion.

Related routes point to the XXE, OAuth/OIDC and auth-bypass skills. This is an offensive playbook, so run it only against systems you are allowed to test.

What it helps with

  • check whether the SP accepts an unsigned SAML assertion
  • find signature wrapping in an IdP XML response
  • compare Audience, Recipient and Destination validation on the SP side
  • reproduce assertion replay when InResponseTo is not enforced
  • trace account binding by email with unverified attributes

Example prompts for the agent

  • walk through the SAML login in this app: which nodes are signed, and can I slip in an unsigned assertion
  • compare the SP-initiated and IdP-initiated flows and show where the Audience checks diverge
  • test replay: weaken NotOnOrAfter and resend the same SAMLResponse

How to install saml-sso-assertion-attacks

1Skills CLI (Vercel)

npx skills add yaklang/hack-skills --skill saml-sso-assertion-attacks -a claude-code

2Manually: put the files in place

~/.claude/skills/saml-sso-assertion-attacks/SKILL.md

Copy the whole skill folder; for one project use .claude/skills/saml-sso-assertion-attacks/

Step by step, with commands for each platform: How to install skills in Claude Code: five ways

Questions about saml-sso-assertion-attacks

How do I install saml-sso-assertion-attacks in Claude?

Run npx skills add yaklang/hack-skills --skill saml-sso-assertion-attacks -a claude-code. The skill lands in ~/.claude/skills/saml-sso-assertion-attacks/SKILL.md.

What does saml-sso-assertion-attacks do?

It gives the agent a playbook for validating SAML assertion trust: signature coverage, audience and recipient checks, ACS handling, XML parsing weaknesses, and IdP/SP confusion.

When does this skill load?

When the target uses SAML-based SSO: SAMLRequest, SAMLResponse, XML assertions or ACS endpoints show up, and login goes through an external IdP.

Source text

SKILL.md · MIT 
---
name: saml-sso-assertion-attacks
description: >-
  SAML SSO assertion attack playbook. Use when testing signature validation, assertion wrapping, audience restrictions, ACS handling, XML trust boundaries, and enterprise SSO flaws.
---

# SKILL: SAML SSO and Assertion Attacks — Signature Validation, Binding, and Trust Confusion

> **AI LOAD INSTRUCTION**: Use this skill when the target uses SAML-based SSO and you need to validate assertion trust: signature coverage, audience and recipient checks, ACS handling, XML parsing weaknesses, and IdP/SP confusion.

## 1. WHEN TO LOAD THIS SKILL

Load when:

- Enterprise SSO uses SAML requests or responses
- You see `SAMLRequest`, `SAMLResponse`, XML assertions, or ACS endpoints
- Login flows involve an external IdP and browser POST/redirect binding

## 2. HIGH-VALUE MISCONFIGURATION CHECKS

| Theme | What to Check |
|---|---|
| signature validation | unsigned assertion accepted, wrong node signed, signature wrapping |
| audience and recipient | weak `Audience`, `Recipient`, `Destination`, or ACS validation |
| issuer trust | wrong IdP accepted or multi-tenant issuer confusion |
| replay and freshness | missing `InResponseTo`, weak `NotBefore` / `NotOnOrAfter` enforcement |
| account mapping | email-only binding, case folding, unverified attributes |
| XML parser behavior | XXE-like parser issues or unsafe transforms around SAML documents |

## 3. QUICK TRIAGE

1. Capture one full login round trip.
2. Inspect which XML nodes are signed and which attributes drive account binding.
3. Compare SP-initiated and IdP-initiated flows.
4. Test replay, altered attributes, and assertion placement confusion.

## 4. RELATED ROUTES

- XML parser attack depth: [xxe xml external entity](../xxe-xml-external-entity/SKILL.md)
- OAuth or OIDC SSO alternatives: [oauth oidc misconfiguration](../oauth-oidc-misconfiguration/SKILL.md)
- Auth boundary issues after SSO: [authbypass authentication flaws](../authbypass-authentication-flaws/SKILL.md)

© yaklang · MIT · yaklang/hack-skills

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