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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
- Capture one full login round trip.
- Inspect which XML nodes are signed and which attributes drive account binding.
- Compare SP-initiated and IdP-initiated flows.
- Test replay, altered attributes, and assertion placement confusion.
4. RELATED ROUTES
- XML parser attack depth: xxe xml external entity
- OAuth or OIDC SSO alternatives: oauth oidc misconfiguration
- Auth boundary issues after SSO: authbypass authentication flaws
