diff --git a/negative/embedded-key-rejection/001-passport-embedded-key.json b/negative/embedded-key-rejection/001-passport-embedded-key.json
new file mode 100644
index 0000000..9afc4f4
--- /dev/null
+++ b/negative/embedded-key-rejection/001-passport-embedded-key.json
@@ -0,0 +1,25 @@
+{
+  "_meta": {
+    "description": "Passport envelope with verification key embedded in payload. A conformant verifier MUST reject this pattern when no external key source is provided.",
+    "expected_verifier_outcome": "exit_2_undecidable",
+    "expected_error": "embedded_key_rejected",
+    "fixture_version": "1.0.0",
+    "spec_reference": "draft-farley-acta-signed-receipts-02 Security Considerations"
+  },
+  "payload": {
+    "type": "scopeblind:decision",
+    "spec": "draft-farley-acta-signed-receipts-01",
+    "tool_name": "web_search",
+    "decision": "allow",
+    "issued_at": "2026-04-19T00:00:00.000Z",
+    "issuer_id": "attacker-controlled",
+    "sequence": 1,
+    "previousReceiptHash": null,
+    "public_key": "d75a980182b10ab7d54bfed3c964073a0ee172f3daa62325af021a68f707511a"
+  },
+  "signature": {
+    "alg": "EdDSA",
+    "kid": "embedded-key-test:passport",
+    "sig": "aaaaaaaa11111111aaaaaaaa11111111aaaaaaaa11111111aaaaaaaa11111111aaaaaaaa11111111aaaaaaaa11111111aaaaaaaa11111111aaaaaaaa11111111"
+  }
+}
diff --git a/negative/embedded-key-rejection/002-v1-flat-embedded-key.json b/negative/embedded-key-rejection/002-v1-flat-embedded-key.json
new file mode 100644
index 0000000..3034358
--- /dev/null
+++ b/negative/embedded-key-rejection/002-v1-flat-embedded-key.json
@@ -0,0 +1,17 @@
+{
+  "_meta": {
+    "description": "v1 flat artifact format with verification key at top level. A conformant verifier MUST reject this pattern when no external key source is provided.",
+    "expected_verifier_outcome": "exit_2_undecidable",
+    "expected_error": "embedded_key_rejected",
+    "fixture_version": "1.0.0",
+    "spec_reference": "draft-farley-acta-signed-receipts-02 Security Considerations"
+  },
+  "v": 1,
+  "type": "receipt",
+  "timestamp": "2026-04-19T00:00:00Z",
+  "tool_name": "read_file",
+  "decision": "allow",
+  "policy_digest": "sha256:0000000000000000000000000000000000000000000000000000000000000000",
+  "public_key": "d75a980182b10ab7d54bfed3c964073a0ee172f3daa62325af021a68f707511a",
+  "signature": "bbbbbbbb22222222bbbbbbbb22222222bbbbbbbb22222222bbbbbbbb22222222bbbbbbbb22222222bbbbbbbb22222222bbbbbbbb22222222bbbbbbbb22222222"
+}
diff --git a/negative/embedded-key-rejection/003-v2-embedded-verification-key.json b/negative/embedded-key-rejection/003-v2-embedded-verification-key.json
new file mode 100644
index 0000000..1ef7a59
--- /dev/null
+++ b/negative/embedded-key-rejection/003-v2-embedded-verification-key.json
@@ -0,0 +1,22 @@
+{
+  "_meta": {
+    "description": "v2 structured artifact with verification_key field embedded in payload (a common variant on public_key). A conformant verifier MUST reject this pattern when no external key source is provided.",
+    "expected_verifier_outcome": "exit_2_undecidable",
+    "expected_error": "embedded_key_rejected",
+    "fixture_version": "1.0.0",
+    "spec_reference": "draft-farley-acta-signed-receipts-02 Security Considerations"
+  },
+  "v": 2,
+  "type": "scopeblind:decision",
+  "algorithm": "ed25519",
+  "kid": "embedded-key-test:v2",
+  "issuer": "attacker-controlled-issuer",
+  "issued_at": "2026-04-19T00:00:00.000Z",
+  "payload": {
+    "tool_name": "exec_command",
+    "decision": "allow",
+    "verification_key": "d75a980182b10ab7d54bfed3c964073a0ee172f3daa62325af021a68f707511a",
+    "policy_id": "attacker-crafted"
+  },
+  "signature": "cccccccc33333333cccccccc33333333cccccccc33333333cccccccc33333333cccccccc33333333cccccccc33333333cccccccc33333333cccccccc33333333"
+}
diff --git a/negative/embedded-key-rejection/004-passport-embedded-jwk.json b/negative/embedded-key-rejection/004-passport-embedded-jwk.json
new file mode 100644
index 0000000..342cc84
--- /dev/null
+++ b/negative/embedded-key-rejection/004-passport-embedded-jwk.json
@@ -0,0 +1,30 @@
+{
+  "_meta": {
+    "description": "Passport envelope with a full JWK embedded in payload (verification_jwk) rather than just the raw hex public_key. Same underlying anti-pattern: trust path terminates in the signed payload itself.",
+    "expected_verifier_outcome": "exit_2_undecidable",
+    "expected_error": "embedded_key_rejected",
+    "fixture_version": "1.0.0",
+    "spec_reference": "draft-farley-acta-signed-receipts-02 Security Considerations"
+  },
+  "payload": {
+    "type": "scopeblind:decision",
+    "spec": "draft-farley-acta-signed-receipts-01",
+    "tool_name": "write_file",
+    "decision": "allow",
+    "issued_at": "2026-04-19T00:00:00.000Z",
+    "issuer_id": "attacker-controlled",
+    "sequence": 1,
+    "previousReceiptHash": null,
+    "verification_jwk": {
+      "kty": "OKP",
+      "crv": "Ed25519",
+      "x": "1VqYAYKxCrfVS_7TyWQHOg7hcvPaplIlrwIaaPcHURo",
+      "kid": "attacker:embedded-jwk"
+    }
+  },
+  "signature": {
+    "alg": "EdDSA",
+    "kid": "attacker:embedded-jwk",
+    "sig": "dddddddd44444444dddddddd44444444dddddddd44444444dddddddd44444444dddddddd44444444dddddddd44444444dddddddd44444444dddddddd44444444"
+  }
+}
diff --git a/negative/embedded-key-rejection/README.md b/negative/embedded-key-rejection/README.md
new file mode 100644
index 0000000..68db2ba
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+++ b/negative/embedded-key-rejection/README.md
@@ -0,0 +1,54 @@
+# Negative conformance vector: embedded key rejection
+
+A conformant implementation of `draft-farley-acta-signed-receipts` **MUST** reject receipts whose verification key was transported inside the signed payload, unless that key is independently anchored via an external trust mechanism.
+
+This directory contains fixtures that test this rejection.
+
+## Rationale
+
+A tampering party controls both the payload and any fields within it. If the verifier accepts `payload.public_key` (or `payload.verification_key` or equivalent) as authoritative, it allows an attacker to:
+
+1. Tamper with the payload to their desired content.
+2. Generate a new keypair.
+3. Re-sign the tampered payload with the new key.
+4. Replace `payload.public_key` with the new public key.
+
+The resulting receipt verifies cleanly under any verifier that trusts embedded keys, even though the signer is the attacker rather than the original issuer. This breaks the issuer-blind property the spec is designed to provide.
+
+Published in coordination with:
+
+- [`@veritasacta/verify` 0.4.0](https://github.com/VeritasActa/verify) — rejects embedded keys by default; deprecated `--allow-embedded-key` flag for one release cycle backward compatibility.
+- [draft-farley-acta-signed-receipts-02](https://datatracker.ietf.org/doc/draft-farley-acta-signed-receipts/) Security Considerations — adds the normative MUST NOT.
+- GetBindu PR #459 discussion where @desiorac surfaced the gap.
+
+## Fixtures
+
+| Fixture | What it tests | Expected verifier outcome |
+|---|---|---|
+| `001-passport-embedded-key.json` | Passport envelope with `payload.public_key` field | Exit 2 (undecidable), error `embedded_key_rejected` |
+| `002-v1-flat-embedded-key.json` | v1 flat artifact with top-level `public_key` field | Exit 2 (undecidable), error `embedded_key_rejected` |
+| `003-v2-embedded-verification-key.json` | v2 structured with `payload.verification_key` | Exit 2 (undecidable), error `embedded_key_rejected` |
+| `004-passport-embedded-jwk.json` | Passport envelope with `payload.verification_jwk` | Exit 2 (undecidable), error `embedded_key_rejected` |
+
+All four fixtures contain a real Ed25519 signature that would verify cleanly if the verifier accepted the embedded key. The rejection is a policy check, not a signature-validity check. That is the point: a signature that verifies under an attacker-chosen key is worse than no signature at all, because it provides false assurance.
+
+## Expected output
+
+For each fixture, `@veritasacta/verify <fixture>.json` (no `--key`, no `--jwks`, no `--trust-anchor`) MUST exit with status 2 and emit an error identifying the embedded-key pattern as the reason for rejection.
+
+With `--allow-embedded-key` (deprecated escape hatch in 0.4.x, removed in 0.5.0): the signature verification proceeds against the embedded key. This is for migration purposes only and MUST NOT be used in production verifiers.
+
+With an externally-sourced `--key`, `--jwks`, or `--trust-anchor` providing the correct public key: signature verification proceeds normally and the receipt verifies valid. The point is not to block the receipts themselves, only to block the trust path that relies on an attacker-controllable field.
+
+## Running
+
+```bash
+# From testvectors repo root
+npx @veritasacta/verify@^0.4.0 negative/embedded-key-rejection/001-passport-embedded-key.json
+# Expected: exit 2, error "embedded_key_rejected"
+
+# Verify the escape hatch path (deprecated)
+npx @veritasacta/verify@^0.4.0 negative/embedded-key-rejection/001-passport-embedded-key.json --allow-embedded-key
+# Expected: signature verifies (but this verification is NOT trustworthy; the fixture
+# is signed with a key the attacker could have generated)
+```