diff --git a/docker-compose.yml b/docker-compose.yml
index 0a30cc2..e0cb150 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -8,7 +8,7 @@ services:
       dockerfile: Dockerfile
     container_name: extension-shield
     ports:
-      - "8007:8007"
+      - "127.0.0.1:8007:8007"  # Localhost only — not accessible from the local network
     volumes:
       # Persist downloaded extensions
       - ./extensions_storage:/app/extensions_storage
diff --git a/docs/GET_STARTED.md b/docs/GET_STARTED.md
index 5ac8c13..86a788c 100644
--- a/docs/GET_STARTED.md
+++ b/docs/GET_STARTED.md
@@ -87,6 +87,8 @@ cp .env.example .env
 docker compose up --build
 # → API at http://localhost:8007
 ```
+
+> **Network note:** The Docker config binds to `127.0.0.1:8007` (localhost only). This means the API is not reachable from other devices on your network. If you need external access (e.g. a shared dev server), change the binding to `0.0.0.0:8007:8007` in `docker-compose.yml` and ensure your firewall rules are appropriate. For production, place the API behind a reverse proxy (nginx, Caddy) rather than exposing it directly.
 </details>
 
 ---
diff --git a/src/extension_shield/api/main.py b/src/extension_shield/api/main.py
index cbcd50c..be55b28 100644
--- a/src/extension_shield/api/main.py
+++ b/src/extension_shield/api/main.py
@@ -389,6 +389,9 @@ async def add_security_headers(request: Request, call_next):
 ANONYMOUS_DAILY_DEEP_SCAN_LIMIT = 1  # anonymous (IP-based) users – after 1 scan, prompt login
 # deep_scan_usage[user_id][YYYY-MM-DD] = used_count
 deep_scan_usage: Dict[str, Dict[str, int]] = {}
+# Lock to prevent race conditions when multiple concurrent requests check/increment the same counter
+import threading as _threading
+_deep_scan_usage_lock = _threading.Lock()
 
 
 def _get_user_id(request: Request) -> str:
@@ -541,13 +544,14 @@ def _deep_scan_limit_status(rate_limit_key: str) -> Dict[str, Any]:
 
 
 def _consume_deep_scan(user_id: str) -> Dict[str, Any]:
-    status = _deep_scan_limit_status(user_id)
-    if status["remaining"] <= 0:
-        return status
-    day_key = status["day_key"]
-    deep_scan_usage.setdefault(user_id, {})
-    deep_scan_usage[user_id][day_key] = deep_scan_usage[user_id].get(day_key, 0) + 1
-    return _deep_scan_limit_status(user_id)
+    with _deep_scan_usage_lock:
+        status = _deep_scan_limit_status(user_id)
+        if status["remaining"] <= 0:
+            return status
+        day_key = status["day_key"]
+        deep_scan_usage.setdefault(user_id, {})
+        deep_scan_usage[user_id][day_key] = deep_scan_usage[user_id].get(day_key, 0) + 1
+        return _deep_scan_limit_status(user_id)
 
 
 def _has_cached_results(extension_id: str) -> bool:
@@ -3080,13 +3084,33 @@ async def get_file_content(extension_id: str, file_path: str, http_request: Requ
     # Construct full file path
     full_path = os.path.join(extracted_path, file_path)
 
-    # Security check: ensure path is within extracted directory
-    if not os.path.abspath(full_path).startswith(os.path.abspath(extracted_path)):
+    # Security check: use commonpath to prevent path traversal bypasses.
+    # os.path.abspath(...).startswith(...) is vulnerable when one path is a
+    # prefix of another directory name (e.g. /tmp/ext_abc vs /tmp/ext_abcdef).
+    abs_full = os.path.abspath(full_path)
+    abs_extracted = os.path.abspath(extracted_path)
+    try:
+        if os.path.commonpath([abs_extracted, abs_full]) != abs_extracted:
+            raise HTTPException(status_code=403, detail="Access denied")
+    except ValueError:
+        # commonpath raises ValueError on Windows when paths are on different drives
         raise HTTPException(status_code=403, detail="Access denied")
 
     if not os.path.exists(full_path):
         raise HTTPException(status_code=404, detail="File not found")
 
+    # Guard against reading very large files into memory (e.g. bundled assets).
+    _MAX_FILE_READ_BYTES = 5 * 1024 * 1024  # 5 MB
+    try:
+        file_size = os.path.getsize(full_path)
+    except OSError:
+        file_size = 0
+    if file_size > _MAX_FILE_READ_BYTES:
+        raise HTTPException(
+            status_code=413,
+            detail=f"File too large to display ({file_size // 1024} KB). Maximum is {_MAX_FILE_READ_BYTES // 1024} KB.",
+        )
+
     try:
         with open(full_path, "r", encoding="utf-8") as f:
             content = f.read()
diff --git a/src/extension_shield/core/manifest_parser.py b/src/extension_shield/core/manifest_parser.py
index e8dc005..0403368 100644
--- a/src/extension_shield/core/manifest_parser.py
+++ b/src/extension_shield/core/manifest_parser.py
@@ -308,6 +308,15 @@ def parse(self) -> Optional[Dict[str, Any]]:
 
         logger.info("Parsing manifest from: %s", manifest_path)
 
+        # Guard against malformed or malicious manifests that are unreasonably large.
+        _MAX_MANIFEST_BYTES = 512 * 1024  # 512 KB
+        manifest_size = manifest_path.stat().st_size
+        if manifest_size > _MAX_MANIFEST_BYTES:
+            raise ValueError(
+                f"manifest.json is too large ({manifest_size} bytes). "
+                f"Maximum allowed size is {_MAX_MANIFEST_BYTES} bytes."
+            )
+
         try:
             with open(manifest_path, "r", encoding="utf-8") as f:
                 raw_manifest = json.load(f)