📝 Docs / Security threat-model + advisory process (#43)

SECURITY.md

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+# Security Policy
+
+`ex_saml` is a SAML 2.0 **Service Provider (SP)** library. It consumes and
+validates IdP-issued SAML responses/assertions and produces SP requests and
+metadata. Because it sits directly on an authentication trust boundary, this
+document states what the library defends against, where the trust boundary
+sits, and how to report issues.
+
+## Supported versions
+
+| Version | Supported |
+|---------|-----------|
+| latest `1.x` | ✅ security fixes |
+| `< 1.0` | ❌ |
+
+## Reporting a vulnerability
+
+Please report suspected vulnerabilities **privately** — do not open a public
+issue for an unpatched flaw.
+
+- Open a [GitHub security advisory](https://github.com/docJerem/ex_saml/security/advisories/new), or
+- email the maintainer (see the repository owner's profile).
+
+Include: affected version, a description, and a proof-of-concept if possible.
+We aim to acknowledge within a few business days and to coordinate a fix and
+disclosure timeline with you.
+
+## Threat model
+
+The SP consumes attacker-reachable input: an IdP `SAMLResponse` POSTed (or
+redirected) to the ACS endpoint. The following classes are explicitly in
+scope.
+
+| Threat | Defense | Where |
+|--------|---------|-------|
+| **XXE / external entities** (external/parameter entities, external DTD) | `:xmerl_scan` is always called with `allow_entities: false` (and `namespace_conformant: true`) | `Core.Binding`, `Core.Sp`, `Metadata` |
+| **Entity-expansion DoS** (billion-laughs) | Same — entity expansion is disabled, so nested/expanding entities cannot be processed | as above |
+| **Signature forgery** | Signatures are verified with `:public_key.verify/4`; a forged/incorrect signature fails | `Core.Xml.Dsig.verify/2` |
+| **Weak signature algorithms** | **RSA-SHA1 is rejected** as cryptographically broken; RSA-SHA256 is accepted | `Core.Xml.Dsig` |
+| **Key substitution via document `KeyInfo`** | Trust is bound to the **configured IdP certificate fingerprints**, never to a document-supplied `KeyInfo`. The certificate carried in the signature is compared against the SP config's `trusted_fingerprints` before the assertion is trusted | `Dsig.check_fingerprints/2`, `IdpData` |
+| **IdP / issuer confusion** | The assertion `Issuer` is validated against the configured IdP `entity_id` when available | `Core.Saml.validate_assertion/4` |
+| **Audience / recipient / destination misuse** | `Recipient` must match the SP ACS; `Audience` is checked against the SP entity id when present | `Core.Saml` |
+| **Time-based replay / stale assertions** | `NotBefore` (with small skew) and `NotOnOrAfter` are enforced | `Core.Saml` |
+| **RelayState / one-time consumption** | Anti-replay of the transaction is delegated to the injected state cache (consumer-provided) | consumer + `ExSaml.State` |
+
+### Trust boundary
+
+> **Signatures are only ever trusted when the signing certificate matches a
+> fingerprint configured for that IdP.** The library never derives trust from
+> data supplied inside the document (e.g. an inline `KeyInfo`/certificate that
+> the response itself carries). This is the single most important invariant:
+> attacker-supplied XML cannot introduce a key the SP will trust.
+
+## Known hardening in progress
+
+These are tracked as open work and are **not yet complete**:
+
+- **XML Signature Wrapping (XSW)** — making the "verified node == consumed
+  node" binding explicit and adding a dedicated XSW test corpus (#39).
+- **Adversarial XML corpus in CI** — a versioned fixture set (XXE, DOCTYPE,
+  entity expansion, encoding, c14n golden outputs) run on every build (#38).
+- **Parsing-surface centralisation + audit gate** — a single hardened parse
+  entry point and a CI check forbidding new unhardened `:xmerl_scan` sites
+  (#32).
+
+## Algorithm policy
+
+| Purpose | Accepted | Rejected |
+|---------|----------|----------|
+| Signature | RSA-SHA256 | RSA-SHA1 (broken) |
+| Digest | SHA-256 | SHA-1 |
+
+## Non-goals
+
+`ex_saml` is a SAML **SP** library only. Out of scope:
+
+- Acting as an Identity Provider (IdP).
+- OIDC / OAuth 2.0 flows.
+- Session management, user storage, or authorization decisions (the consuming
+  application owns these).
+- Transport security (TLS termination), which is the deployment's
+  responsibility.
+
+## Coordinated disclosure
+
+We follow coordinated disclosure. After a fix ships, a write-up is published
+under [`docs/advisories/`](docs/advisories/) following
+[`docs/advisories/TEMPLATE.md`](docs/advisories/TEMPLATE.md): root cause,
+impact, affected versions, and the fix.

docs/advisories/TEMPLATE.md

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+# Advisory: <short title>
+
+- **Identifier:** GHSA-xxxx / CVE-xxxx (if assigned)
+- **Severity:** Critical | High | Medium | Low
+- **Affected versions:** `>= x.y.z, < a.b.c`
+- **Fixed in:** `a.b.c`
+- **Reported by:** <name / anonymous>
+- **Published:** YYYY-MM-DD
+
+## Summary
+
+One or two sentences: what the flaw is and the impact in plain terms.
+
+## Root cause
+
+The technical cause — the code path, the missing/incorrect check, and why it
+was exploitable. Reference the relevant module/function.
+
+## Impact
+
+What an attacker can achieve (e.g. authentication bypass, DoS, information
+disclosure), and under what preconditions.
+
+## Proof of concept
+
+Minimal reproduction (redacted as needed).
+
+## Fix
+
+What changed and why it closes the issue. Link the PR/commit.
+
+## Mitigation / workaround
+
+Any interim mitigation for users who cannot upgrade immediately.
+
+## Timeline
+
+- YYYY-MM-DD — reported
+- YYYY-MM-DD — fix merged
+- YYYY-MM-DD — release published
+- YYYY-MM-DD — advisory published

mix.lock

@@ -18,7 +18,7 @@
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