diff --git a/known-issues.md b/known-issues.md
index cf30fb8..af96770 100644
--- a/known-issues.md
+++ b/known-issues.md
@@ -130,10 +130,11 @@ and only write to disk as a recovery fallback.
 
 ---
 
-## KI-005 — `validate_plugin` does not check for secrets in bundle manifests
+## KI-005 — `validate_manifest` does not check for secrets in bundle manifests
 
 **File:** `molecule_plugin/manifest.py:validate_manifest`  
-**Status:** Not yet implemented  
+**Status:** ✅ Fixed — `_scan_for_secrets()` added; called from `validate_manifest`  
+**Resolved in:** `fix/ki-005-ki-007` branch  
 **Severity:** High
 
 ### Symptom
@@ -191,7 +192,8 @@ the plugin content.
 ## KI-007 — `_is_hex` raises `TypeError` on non-string arguments instead of returning `False`
 
 **File:** `molecule_agent/client.py:_is_hex`  
-**Status:** Identified  
+**Status:** ✅ Fixed — isinstance guard added  
+**Resolved in:** `fix/ki-005-ki-007` branch  
 **Severity:** Low
 
 ### Symptom
diff --git a/molecule_agent/client.py b/molecule_agent/client.py
index d378878..e0ee142 100644
--- a/molecule_agent/client.py
+++ b/molecule_agent/client.py
@@ -162,6 +162,8 @@ def verify_plugin_sha256(plugin_dir: Path, expected: str) -> bool:
 
 
 def _is_hex(value: str) -> bool:
+    if not isinstance(value, str):
+        return False
     try:
         int(value, 16)
         return True
diff --git a/molecule_plugin/manifest.py b/molecule_plugin/manifest.py
index 8e191ce..50a53cc 100644
--- a/molecule_plugin/manifest.py
+++ b/molecule_plugin/manifest.py
@@ -105,9 +105,68 @@ def validate_manifest(path: str | Path) -> list[str]:
                 "`sha256` must contain only lowercase hex characters (0–9, a–f)"
             )
 
+    # Secrets scan — no credentials may appear in any string value
+    for field_name, field_value in raw.items():
+        _scan_for_secrets(field_name, field_value, errors)
+
     return errors
 
 
+# ---------------------------------------------------------------------------
+# Secrets scanning
+# ---------------------------------------------------------------------------
+
+# Patterns matching common credential formats.
+# Anchored with word boundaries where possible to avoid false positives
+# in legitimate content (e.g. "sk" inside "ask").
+_SECRET_PATTERNS: list[tuple[str, re.Pattern[str]]] = [
+    # AWS / GCP / Azure keys
+    ("AWS key pattern", re.compile(r"AKIA[0-9A-Z]{16}")),
+    # GitHub fine-grained / classic tokens
+    ("GitHub token", re.compile(r"gh[pousr]_[A-Za-z0-9_]{36,}")),
+    # GitHub app token
+    ("GitHub app token", re.compile(r"gho_[A-Za-z0-9_]{36}")),
+    # OpenAI / Anthropic / generic sk- keys
+    ("OpenAI/Anthropic key", re.compile(r"\bsk-[A-Za-z0-9_-]{20,}\b")),
+    # Bearer tokens in JSON/YAML values
+    ("Bearer token", re.compile(r'"[Bb]earer\s+[A-Za-z0-9_.-]+"')),
+    # Long hex strings that look like cryptographic keys (32+ bytes)
+    ("long hex secret", re.compile(r"\b[0-9a-fA-F]{64,}\b")),
+    # Password assignment patterns in YAML values
+    ("password assignment", re.compile(r"(?i)password\s*[=:]\s*['\"]?[A-Za-z0-9_/+=.-]{8,}")),
+    # API key assignment patterns
+    ("api_key assignment", re.compile(r"(?i)api[_-]?key\s*[=:]\s*['\"]?[A-Za-z0-9_/+=.-]{16,}")),
+    # Secret / token assignment patterns
+    ("secret assignment", re.compile(r"(?i)secret\s*[=:]\s*['\"]?[A-Za-z0-9_/+=.-]{16,}")),
+    # Generic bearer string in raw text
+    ("raw bearer", re.compile(r"Bearer [A-Za-z0-9_.-]{20,}")),
+]
+
+
+def _scan_for_secrets(key: str, value: Any, errors: list[str]) -> None:
+    """Recursively scan `value` (and all nested values) for secret patterns.
+
+    Appends error messages to `errors` when a match is found.
+    Skips `sha256` field since it's a content-addressed hash, not a secret.
+    """
+    if key in ("sha256",):
+        return
+    if isinstance(value, str):
+        for description, pattern in _SECRET_PATTERNS:
+            if pattern.search(value):
+                errors.append(
+                    f"possible secret detected in `{key}`: {description} — "
+                    "bundles must not contain credentials; use platform secrets instead"
+                )
+                break  # report first match only to keep noise minimal
+    elif isinstance(value, dict):
+        for k, v in value.items():
+            _scan_for_secrets(k, v, errors)
+    elif isinstance(value, list):
+        for i, item in enumerate(value):
+            _scan_for_secrets(f"{key}[{i}]", item, errors)
+
+
 # ---------------------------------------------------------------------------
 # agentskills.io spec — SKILL.md validation
 # ---------------------------------------------------------------------------
diff --git a/tests/test_sha256_verification.py b/tests/test_sha256_verification.py
index 4312088..eb1d6b2 100644
--- a/tests/test_sha256_verification.py
+++ b/tests/test_sha256_verification.py
@@ -52,17 +52,15 @@ def test_is_hex_invalid_char():
 
 
 def test_is_hex_non_string():
-    """Non-strings fed to _is_hex must not raise unhandled TypeError.
+    """Non-strings fed to _is_hex return False cleanly, not raise TypeError.
 
-    Python's int(None, 16) raises TypeError. The SDK implementation does not
-    guard with isinstance(value, str) first, so non-string values raise TypeError.
-    This test documents the current (unguarded) behaviour. A follow-up should add
-    isinstance(value, str) guard to _is_hex so it returns False cleanly.
+    Python's int(None, 16) raises TypeError. The SDK implementation guards
+    with isinstance(value, str) first, so non-string values return False
+    rather than surfacing a confusing TypeError.
     """
     for val in (None, 123, [], {}):
-        # Currently raises TypeError — documents known gap
-        with pytest.raises(TypeError):
-            _is_hex(val)
+        # After the isinstance guard, non-strings return False cleanly
+        assert _is_hex(val) is False
 
 
 # ---------------------------------------------------------------------------