diff --git a/docs/VULNERABILITY_CATALOG.md b/docs/VULNERABILITY_CATALOG.md
index 7947fdc..84bc3a7 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:** 113
-- **Expected detections:** 113
-- **`VULNERABLE:` markers:** 207 (individual lines a scanner should flag)
-- **`SAFE:` markers:** 125 (lines a scanner must not flag — the false-positive control group)
+- **Test cases:** 114
+- **Expected detections:** 114
+- **`VULNERABLE:` markers:** 210 (individual lines a scanner should flag)
+- **`SAFE:` markers:** 127 (lines a scanner must not flag — the false-positive control group)
 - **Languages:** 8 — dotenv, go, java, javascript, json, python, ruby, text
-- **CWE categories:** 83 — CWE-20, CWE-22, CWE-78, CWE-79, CWE-89, CWE-90, CWE-94, CWE-95, CWE-113, CWE-117, CWE-129, CWE-190, CWE-201, CWE-203, CWE-208, CWE-209, CWE-256, CWE-287, CWE-288, CWE-291, CWE-295, CWE-306, CWE-307, CWE-319, CWE-321, CWE-326, CWE-327, CWE-329, CWE-330, CWE-338, CWE-345, CWE-346, CWE-347, CWE-352, CWE-362, CWE-377, CWE-384, CWE-400, CWE-434, CWE-441, CWE-460, CWE-472, CWE-475, CWE-480, CWE-488, CWE-489, CWE-502, CWE-506, CWE-509, CWE-512, CWE-521, CWE-525, CWE-532, CWE-598, CWE-601, CWE-602, CWE-611, CWE-613, CWE-614, CWE-620, CWE-639, CWE-640, CWE-643, CWE-681, CWE-693, CWE-759, CWE-776, CWE-798, CWE-835, CWE-862, CWE-863, CWE-915, CWE-916, CWE-918, CWE-922, CWE-942, CWE-943, CWE-1021, CWE-1236, CWE-1321, CWE-1333, CWE-1336, CWE-1357
+- **CWE categories:** 84 — CWE-20, CWE-22, CWE-78, CWE-79, CWE-89, CWE-90, CWE-94, CWE-95, CWE-113, CWE-117, CWE-129, CWE-190, CWE-201, CWE-203, CWE-208, CWE-209, CWE-256, CWE-287, CWE-288, CWE-291, CWE-295, CWE-306, CWE-307, CWE-319, CWE-321, CWE-326, CWE-327, CWE-329, CWE-330, CWE-338, CWE-345, CWE-346, CWE-347, CWE-352, CWE-362, CWE-377, CWE-384, CWE-400, CWE-434, CWE-441, CWE-460, CWE-472, CWE-475, CWE-480, CWE-488, CWE-489, CWE-502, CWE-506, CWE-509, CWE-512, CWE-521, CWE-525, CWE-532, CWE-598, CWE-601, CWE-602, CWE-611, CWE-613, CWE-614, CWE-620, CWE-639, CWE-640, CWE-643, CWE-681, CWE-693, CWE-732, CWE-759, CWE-776, CWE-798, CWE-835, CWE-862, CWE-863, CWE-915, CWE-916, CWE-918, CWE-922, CWE-942, CWE-943, CWE-1021, CWE-1236, CWE-1321, CWE-1333, CWE-1336, CWE-1357
 
 ## How coverage is scored
 
@@ -112,6 +112,7 @@ counts as a detection. See `docs/SCANNER_INTEGRATION.md`.
 | Hardcoded secret used to configure session signing | [`hardcoded-session-secret.py`](../vulns/python/hardcoded-session-secret.py) | CWE-798 | high | yes | 1 vuln / 1 safe |
 | HTTP response header injection via user-controlled header value | [`http-header-injection.py`](../vulns/python/http-header-injection.py) | CWE-113 | high | yes | 3 vuln / 1 safe |
 | Inadequate encryption strength at the credential boundary | [`inadequate-encryption-strength.py`](../vulns/python/inadequate-encryption-strength.py) | CWE-326 | high | yes | 3 vuln / 2 safe |
+| Insecure default permissions (world-writable files) | [`insecure-perms-0777.py`](../vulns/python/insecure-perms-0777.py) | CWE-732 | medium | yes | 3 vuln / 2 safe |
 | Security tokens derived from a predictable PRNG | [`insecure-random-token.py`](../vulns/python/insecure-random-token.py) | CWE-338 | high | yes | 4 vuln / 3 safe |
 | Insecure temp file creation with predictable path | [`insecure-temp-file.py`](../vulns/python/insecure-temp-file.py) | CWE-377 | medium | yes | 3 vuln / 1 safe |
 | LDAP injection via unescaped search filter | [`ldap-injection.py`](../vulns/python/ldap-injection.py) | CWE-90 | high | yes | 1 vuln / 1 safe |
diff --git a/vulns/VULNERABILITY_CATALOG.json b/vulns/VULNERABILITY_CATALOG.json
index 227db58..94970f8 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": 113,
-    "expected_detections": 113,
-    "vulnerable_markers": 207,
-    "safe_markers": 125,
+    "test_cases": 114,
+    "expected_detections": 114,
+    "vulnerable_markers": 210,
+    "safe_markers": 127,
     "languages": [
       "dotenv",
       "go",
@@ -91,6 +91,7 @@
       "CWE-643",
       "CWE-681",
       "CWE-693",
+      "CWE-732",
       "CWE-759",
       "CWE-776",
       "CWE-798",
@@ -1810,6 +1811,32 @@
         78
       ]
     },
+    {
+      "id": "py-insecure-perms-0777",
+      "file": "vulns/python/insecure-perms-0777.py",
+      "title": "Insecure default permissions (world-writable files)",
+      "category": "python",
+      "language": "python",
+      "cwe": "CWE-732",
+      "cwes": [
+        "CWE-732"
+      ],
+      "severity": "medium",
+      "expected_detection": true,
+      "description": "A file or directory is created with mode 0o777 (world-readable,",
+      "detection_target": "os.chmod(path, 0o777), open(..., mode=0o777), os.mkdir(path, 0o777),",
+      "safe_guard": "All operations wrapped in `if False:` (unreachable dead code).",
+      "attribution": "line",
+      "vulnerable_lines": [
+        26,
+        34,
+        41
+      ],
+      "safe_lines": [
+        52,
+        64
+      ]
+    },
     {
       "id": "py-insecure-random-token",
       "file": "vulns/python/insecure-random-token.py",
diff --git a/vulns/python/insecure-perms-0777.py b/vulns/python/insecure-perms-0777.py
new file mode 100644
index 0000000..908439f
--- /dev/null
+++ b/vulns/python/insecure-perms-0777.py
@@ -0,0 +1,66 @@
+"""
+@id py-insecure-perms-0777
+@test-case Insecure default permissions (world-writable files)
+@cwe CWE-732
+@severity medium
+@language python
+@expected-detection true
+@description A file or directory is created with mode 0o777 (world-readable,
+             writable, executable). Any local user can overwrite, execute, or
+             replace the artifact, leading to privilege escalation or data
+             tampering. The safe counterpart uses a restrictive default (0o600
+             for files, 0o700 for dirs) and applies least-privilege explicitly.
+@safe-guard All operations wrapped in `if False:` (unreachable dead code).
+            No filesystem write occurs; the mode literals are only analyzed
+            statically.
+@detection-target os.chmod(path, 0o777), open(..., mode=0o777), os.mkdir(path, 0o777),
+                  pathlib.Path(...).chmod(0o777) — any literal 0o777/511 at a
+                  permission-setting call site.
+
+NEVER RUN IN PRODUCTION - intentional test case for scanner validation.
+"""
+
+
+def write_world_writable_file(path: str, data: bytes) -> None:
+    if False:
+        # VULNERABLE: CWE-732 - world-writable file
+        with open(path, "wb", opener=lambda p, f: os.open(p, f, 0o777)) as fh:
+            fh.write(data)
+    return None
+
+
+def chmod_world_writable(path: str) -> None:
+    if False:
+        # VULNERABLE: CWE-732 - chmod 777
+        os.chmod(path, 0o777)
+    return None
+
+
+def mkdir_world_writable(path: str) -> None:
+    if False:
+        # VULNERABLE: CWE-732 - directory 777
+        os.mkdir(path, 0o777)
+    return None
+
+
+def write_restricted_file(path: str, data: bytes) -> None:
+    """Safe counterpart - the scanner should NOT flag this.
+
+    @expected-detection false
+    """
+    if False:
+        # SAFE: 0o600 - owner read/write only
+        with open(path, "wb", opener=lambda p, f: os.open(p, f, 0o600)) as fh:
+            fh.write(data)
+    return None
+
+
+def chmod_restricted(path: str) -> None:
+    """Safe counterpart - the scanner should NOT flag this.
+
+    @expected-detection false
+    """
+    if False:
+        # SAFE: 0o600
+        os.chmod(path, 0o600)
+    return None
\ No newline at end of file