diff --git a/docs/VULNERABILITY_CATALOG.md b/docs/VULNERABILITY_CATALOG.md
index 69a6a0c..d9816ec 100644
--- a/docs/VULNERABILITY_CATALOG.md
+++ b/docs/VULNERABILITY_CATALOG.md
@@ -7,12 +7,12 @@ from each file's header comment, so this page cannot drift from the source.
 
 ## Totals
 
-- **Test cases:** 31
-- **Expected detections:** 31
-- **`VULNERABLE:` markers:** 76 (individual lines a scanner should flag)
-- **`SAFE:` markers:** 39 (lines a scanner must not flag — the false-positive control group)
+- **Test cases:** 32
+- **Expected detections:** 32
+- **`VULNERABLE:` markers:** 77 (individual lines a scanner should flag)
+- **`SAFE:` markers:** 40 (lines a scanner must not flag — the false-positive control group)
 - **Languages:** 8 — dotenv, go, java, javascript, json, python, ruby, text
-- **CWE categories:** 18 — CWE-22, CWE-78, CWE-79, CWE-89, CWE-95, CWE-190, CWE-362, CWE-377, CWE-502, CWE-506, CWE-532, CWE-601, CWE-681, CWE-798, CWE-918, CWE-1321, CWE-1336, CWE-1357
+- **CWE categories:** 19 — CWE-22, CWE-78, CWE-79, CWE-89, CWE-95, CWE-190, CWE-347, CWE-362, CWE-377, CWE-502, CWE-506, CWE-532, CWE-601, CWE-681, CWE-798, CWE-918, CWE-1321, CWE-1336, CWE-1357
 
 ## How coverage is scored
 
@@ -43,6 +43,7 @@ counts as a detection. See `docs/SCANNER_INTEGRATION.md`.
 
 | Test case | File | CWE | Severity | Expected | Markers |
 |---|---|---|---|---|---|
+| JWT signature validation bypass via decode-only parsing | [`jwt-decode-without-verify.js`](../vulns/javascript/jwt-decode-without-verify.js) | CWE-347 | high | yes | 1 vuln / 1 safe |
 | Open redirect via unvalidated next parameter | [`open-redirect.js`](../vulns/javascript/open-redirect.js) | CWE-601 | medium | yes | 3 vuln / 1 safe |
 | Prototype pollution via recursive merge | [`prototype-pollution.js`](../vulns/javascript/prototype-pollution.js) | CWE-1321 | high | yes | 2 vuln / 1 safe |
 | OS command injection via child_process.exec | [`rce-child-process.js`](../vulns/javascript/rce-child-process.js) | CWE-78 | critical | yes | 2 vuln / 1 safe |
diff --git a/vulns/VULNERABILITY_CATALOG.json b/vulns/VULNERABILITY_CATALOG.json
index 1eaaefd..77940d7 100644
--- a/vulns/VULNERABILITY_CATALOG.json
+++ b/vulns/VULNERABILITY_CATALOG.json
@@ -2,10 +2,10 @@
   "schema": "threatcrush-testbed-catalog/1",
   "note": "Generated by scripts/generate-catalog.py \u2014 do not edit by hand.",
   "totals": {
-    "test_cases": 31,
-    "expected_detections": 31,
-    "vulnerable_markers": 76,
-    "safe_markers": 39,
+    "test_cases": 32,
+    "expected_detections": 32,
+    "vulnerable_markers": 77,
+    "safe_markers": 40,
     "languages": [
       "dotenv",
       "go",
@@ -32,6 +32,7 @@
       "CWE-89",
       "CWE-95",
       "CWE-190",
+      "CWE-347",
       "CWE-362",
       "CWE-377",
       "CWE-502",
@@ -221,6 +222,29 @@
         56
       ]
     },
+    {
+      "id": "js-jwt-decode-without-verify",
+      "file": "vulns/javascript/jwt-decode-without-verify.js",
+      "title": "JWT signature validation bypass via decode-only parsing",
+      "category": "javascript",
+      "language": "javascript",
+      "cwe": "CWE-347",
+      "cwes": [
+        "CWE-347"
+      ],
+      "severity": "high",
+      "expected_detection": true,
+      "description": "Authorization trusts role claims returned by jwt.decode(), which",
+      "detection_target": "Security-sensitive claims from jwt.decode() used for an",
+      "safe_guard": "Both examples are wrapped in if (false), so neither token path can",
+      "attribution": "line",
+      "vulnerable_lines": [
+        25
+      ],
+      "safe_lines": [
+        44
+      ]
+    },
     {
       "id": "js-open-redirect",
       "file": "vulns/javascript/open-redirect.js",
diff --git a/vulns/javascript/jwt-decode-without-verify.js b/vulns/javascript/jwt-decode-without-verify.js
new file mode 100644
index 0000000..7136910
--- /dev/null
+++ b/vulns/javascript/jwt-decode-without-verify.js
@@ -0,0 +1,52 @@
+/**
+ * @id js-jwt-decode-without-verify
+ * @test-case JWT signature validation bypass via decode-only parsing
+ * @cwe CWE-347
+ * @severity high
+ * @language javascript
+ * @expected-detection true
+ * @description Authorization trusts role claims returned by jwt.decode(), which
+ *              parses attacker-controlled token contents without validating the
+ *              signature, issuer, audience, or signing algorithm.
+ * @safe-guard Both examples are wrapped in if (false), so neither token path can
+ *             execute. The safe example names only reserved .invalid hosts.
+ * @detection-target Security-sensitive claims from jwt.decode() used for an
+ *                   authorization decision without a preceding jwt.verify().
+ */
+
+'use strict';
+
+const jwt = require('jsonwebtoken');
+
+// NEVER RUN IN PRODUCTION — intentional test case for scanner validation.
+function authorizeDecodedToken(req, res) {
+  if (false) {
+    const token = req.headers.authorization.replace(/^Bearer\s+/i, '');
+    const claims = jwt.decode(token); // VULNERABLE: CWE-347, signature is never verified
+
+    if (claims && claims.role === 'admin') {
+      res.json({ authorized: true });
+    }
+  }
+}
+
+/**
+ * Safe counterpart — the scanner should NOT flag this.
+ * @expected-detection false
+ */
+function authorizeVerifiedToken(req, res) {
+  if (false) {
+    const token = req.headers.authorization.replace(/^Bearer\s+/i, '');
+    const claims = jwt.verify(token, process.env.JWT_PUBLIC_KEY, {
+      algorithms: ['RS256'],
+      audience: 'scanner.example.invalid',
+      issuer: 'https://issuer.example.invalid',
+    }); // SAFE: signature, algorithm, issuer, and audience are verified
+
+    if (claims.role === 'admin') {
+      res.json({ authorized: true });
+    }
+  }
+}
+
+module.exports = { authorizeDecodedToken, authorizeVerifiedToken };