diff --git a/routes/admin.py b/routes/admin.py
index 4470ea8..c1b3f66 100644
--- a/routes/admin.py
+++ b/routes/admin.py
@@ -196,6 +196,11 @@ def admin_get_user_servers(user_id):
             return jsonify({'success': False, 'error': 'Admin access required'}), 403
 
         servers = get_user_servers(user_id)
+        # Admin server management does not need connection credentials.
+        servers = [
+            {key: value for key, value in server.items() if key != 'sftp_password'}
+            for server in servers
+        ]
         return jsonify({'success': True, 'servers': servers}), 200
 
     except Exception as e:
@@ -331,7 +336,7 @@ def admin_get_all_servers():
             cursor.execute('''
                 SELECT s.id, s.name, s.cpu, s.ram, s.storage, s.image, s.type, s.version, s.loader, s.java_version,
                        s.status, s.ports, s.created_at, u.username as owner, u.id as owner_id,
-                       s.sftp_username, s.sftp_password, s.sftp_port
+                       s.sftp_username, s.sftp_port
                 FROM servers s
                 JOIN users u ON s.owner_id = u.id
                 ORDER BY u.username, s.name
diff --git a/routes/servers.py b/routes/servers.py
index 2c269a6..cba8712 100644
--- a/routes/servers.py
+++ b/routes/servers.py
@@ -4,8 +4,10 @@
 from datetime import datetime
 from flask import Blueprint, jsonify, request
 import json
+from urllib.parse import urlsplit
 from kubernetes_service import k8s_manager
 import requests
+from werkzeug.utils import secure_filename
 from runtime_config import (
     MODRINTH_API_BASE,
     logger,
@@ -317,6 +319,21 @@ def download_plugin_to_server():
         if not server_id or not plugin_url:
             return jsonify({'error': 'Server ID and plugin URL are required'}), 400
 
+        try:
+            parsed_plugin_url = urlsplit(plugin_url)
+            plugin_port = parsed_plugin_url.port
+        except (TypeError, ValueError):
+            return jsonify({'error': 'Plugin URL is invalid'}), 400
+        if (parsed_plugin_url.scheme != 'https'
+                or parsed_plugin_url.hostname != 'cdn.modrinth.com'
+                or parsed_plugin_url.username or parsed_plugin_url.password
+                or plugin_port not in (None, 443)):
+            return jsonify({'error': 'Plugin files must come from the Modrinth CDN'}), 400
+
+        safe_file_name = secure_filename(str(file_name or 'plugin.jar'))
+        if not safe_file_name.lower().endswith('.jar'):
+            return jsonify({'error': 'Plugin file name must end in .jar'}), 400
+
         # Verify server belongs to user
         user_servers = get_user_servers(user['id'])
         server = next((s for s in user_servers if s['id'] == server_id), None)
@@ -330,26 +347,37 @@ def download_plugin_to_server():
 
         # Download plugin file
         logger.info(f"Downloading plugin from {plugin_url} for server {server_id}")
-        plugin_response = requests.get(plugin_url, stream=True, timeout=30)
+        plugin_response = requests.get(
+            plugin_url, stream=True, timeout=30, allow_redirects=False
+        )
 
         if plugin_response.status_code != 200:
+            plugin_response.close()
             return jsonify({'error': f'Failed to download plugin: HTTP {plugin_response.status_code}'}), 500
 
         # Determine plugins directory based on server type
         # For Minecraft servers, plugins go in /data/plugins directory
         plugins_dir = '/data/plugins'
-        file_path = f'{plugins_dir}/{file_name}'
+        file_path = f'{plugins_dir}/{safe_file_name}'
 
         # Save plugin to temporary file first
         import tempfile
         import os
-        with tempfile.NamedTemporaryFile(delete=False, suffix='.jar') as temp_file:
-            temp_file_path = temp_file.name
-            for chunk in plugin_response.iter_content(chunk_size=8192):
-                if chunk:
-                    temp_file.write(chunk)
-
+        temp_file = tempfile.NamedTemporaryFile(delete=False, suffix='.jar')
+        temp_file_path = temp_file.name
         try:
+            with temp_file:
+                try:
+                    total_bytes = 0
+                    for chunk in plugin_response.iter_content(chunk_size=8192):
+                        if chunk:
+                            total_bytes += len(chunk)
+                            if total_bytes > 100 * 1024 * 1024:
+                                raise ValueError('Plugin file exceeds the 100 MB limit')
+                            temp_file.write(chunk)
+                finally:
+                    plugin_response.close()
+
             # Upload to server
             namespace = f"user-{user['username']}".lower()
             pods = k8s_manager.get_pods_for_server(namespace, server_id)