fix(security): consolidation & securite phase 1 (#84, BUG-021 a BUG-034)

- sanitizer XSS serveur (markdown + page de partage) [BUG-021/022]
- rate-limit/lockout MFA [BUG-023]
- isolation vaults par segments [BUG-024]
- caps regex ReDoS [BUG-025]
- SSRF webhooks + secrets externalises [BUG-026]
- rotation/revocation des jetons [BUG-027]
- politique de mot de passe + invalidation sessions [BUG-028]
- verrous users.json [BUG-029]
- IP reelle dans les audits [BUG-030]
- rate-limit par compte [BUG-031]
- symlinks hors vault ignores [BUG-032]
- recherche simple via inverted index [BUG-033]
- token en memoire + cookie HttpOnly, CSP durcie [BUG-034]

Tests: pytest 961 passed / 6 skipped, ruff 0, mypy 0, frontend vert.

backend/auth/user_store.py

@@ -6,6 +6,7 @@
 import json
 import logging
 import shutil
+import threading
 import uuid
 from datetime import datetime, timedelta, timezone
 from pathlib import Path
@@ -16,6 +17,12 @@ logger = logging.getLogger("obsigate.auth.users")
 
 USERS_FILE = Path("data/users.json")
 
+# Serialises read-modify-write cycles on users.json.  ``RLock`` because a few
+# helpers (e.g. ``record_login_failure``) call other mutators while holding it.
+# BUG-029: without this, concurrent MFA enable + password change could lose one
+# of the two updates (last writer wins).
+_users_lock = threading.RLock()
+
 
 def _read() -> dict:
     """Read users.json. Returns empty structure if file doesn't exist."""
@@ -75,26 +82,28 @@ def create_user(
     display_name: str | None = None,
 ) -> dict:
     """Create a new user. Raises ValueError if username already taken."""
-    data = _read()
-    if username in data["users"]:
-        raise ValueError(f"User '{username}' already exists")
+    with _users_lock:
+        data = _read()
+        if username in data["users"]:
+            raise ValueError(f"User '{username}' already exists")
 
-    user = {
-        "id": str(uuid.uuid4()),
-        "username": username,
-        "display_name": display_name or username,
-        "password_hash": hash_password(password),
-        "role": role,
-        "vaults": vaults or [],
-        "active": True,
-        "language": "fr",  # default UI language
-        "created_at": datetime.now(timezone.utc).isoformat(),
-        "last_login": None,
-        "failed_attempts": 0,
-        "locked_until": None,
-    }
-    data["users"][username] = user
-    _write(data)
+        user = {
+            "id": str(uuid.uuid4()),
+            "username": username,
+            "display_name": display_name or username,
+            "password_hash": hash_password(password),
+            "role": role,
+            "vaults": vaults or [],
+            "active": True,
+            "language": "fr",  # default UI language
+            "created_at": datetime.now(timezone.utc).isoformat(),
+            "password_changed_at": datetime.now(timezone.utc).timestamp(),
+            "last_login": None,
+            "failed_attempts": 0,
+            "locked_until": None,
+        }
+        data["users"][username] = user
+        _write(data)
     logger.info(f"Created user '{username}' (role={role})")
     return {k: v for k, v in user.items() if k != "password_hash"}
 
@@ -105,28 +114,33 @@ def update_user(username: str, updates: dict) -> dict:
     Forbidden fields (id, username, created_at) are silently ignored.
     If 'password' is in updates, it's hashed and stored as password_hash.
     """
-    data = _read()
-    if username not in data["users"]:
-        raise ValueError(f"User '{username}' not found")
+    with _users_lock:
+        data = _read()
+        if username not in data["users"]:
+            raise ValueError(f"User '{username}' not found")
 
-    forbidden = {"id", "username", "created_at"}
-    safe_updates = {k: v for k, v in updates.items() if k not in forbidden}
+        forbidden = {"id", "username", "created_at"}
+        safe_updates = {k: v for k, v in updates.items() if k not in forbidden}
 
-    if "password" in safe_updates:
-        safe_updates["password_hash"] = hash_password(safe_updates.pop("password"))
+        if "password" in safe_updates:
+            safe_updates["password_hash"] = hash_password(safe_updates.pop("password"))
+            # BUG-028: invalidate every token issued before this change.
+            safe_updates["password_changed_at"] = datetime.now(timezone.utc).timestamp()
 
-    data["users"][username].update(safe_updates)
-    _write(data)
-    return {k: v for k, v in data["users"][username].items() if k != "password_hash"}
+        data["users"][username].update(safe_updates)
+        _write(data)
+        result = {k: v for k, v in data["users"][username].items() if k != "password_hash"}
+    return result
 
 
 def delete_user(username: str):
     """Delete a user. Raises ValueError if not found."""
-    data = _read()
-    if username not in data["users"]:
-        raise ValueError(f"User '{username}' not found")
-    del data["users"][username]
-    _write(data)
+    with _users_lock:
+        data = _read()
+        if username not in data["users"]:
+            raise ValueError(f"User '{username}' not found")
+        del data["users"][username]
+        _write(data)
     logger.info(f"Deleted user '{username}'")
 
 
@@ -144,24 +158,25 @@ def record_login_failure(username: str) -> int:
 
     After 5 failures, locks the account for 15 minutes.
     """
-    data = _read()
-    user = data["users"].get(username)
-    if not user:
-        return 0
+    with _users_lock:
+        data = _read()
+        user = data["users"].get(username)
+        if not user:
+            return 0
 
-    attempts = user.get("failed_attempts", 0) + 1
-    updates = {"failed_attempts": attempts}
+        attempts = user.get("failed_attempts", 0) + 1
+        updates = {"failed_attempts": attempts}
 
-    # Lock after 5 failed attempts (15 minutes)
-    if attempts >= 5:
-        locked_until = (
-            datetime.now(timezone.utc) + timedelta(minutes=15)
-        ).isoformat()
-        updates["locked_until"] = locked_until
-        logger.warning(f"Account '{username}' locked after {attempts} failed attempts")
+        # Lock after 5 failed attempts (15 minutes)
+        if attempts >= 5:
+            locked_until = (
+                datetime.now(timezone.utc) + timedelta(minutes=15)
+            ).isoformat()
+            updates["locked_until"] = locked_until
+            logger.warning(f"Account '{username}' locked after {attempts} failed attempts")
 
-    update_user(username, updates)
-    return attempts
+        update_user(username, updates)
+        return attempts
 
 
 def is_locked(username: str) -> bool: