diff --git a/common.py b/common.py
index 14bc735..ec6adf3 100644
--- a/common.py
+++ b/common.py
@@ -132,6 +132,9 @@ async def oauth_authorize(request: Request):
     if not code_challenge:
         return HTMLResponse("<h1>Fehler</h1><p>PKCE erforderlich (code_challenge fehlt).</p>", status_code=400)
 
+    if not redirect_uri.startswith(("https://claude.ai/", "https://claude.com/")):
+        return HTMLResponse("<h1>Fehler</h1><p>Ungueltige redirect_uri.</p>", status_code=400)
+
     code = secrets.token_urlsafe(32)
     _auth_codes[code] = {
         "client_id": client_id,
diff --git a/mail/server.py b/mail/server.py
index 0932870..661caf5 100644
--- a/mail/server.py
+++ b/mail/server.py
@@ -161,7 +161,11 @@ def _discover_folders(acct_path):
 
 
 def _open_folder(acct_path, folder_name):
-    path = os.path.join(acct_path, folder_name)
+    base = os.path.realpath(acct_path)
+    path = os.path.realpath(os.path.join(base, folder_name))
+    # Path-Traversal verhindern: muss innerhalb des Account-Verzeichnisses bleiben
+    if path != base and not path.startswith(base + os.sep):
+        return None
     return mailbox.Maildir(path, create=False) if os.path.isdir(path) else None
 
 
diff --git a/tests/test_all.py b/tests/test_all.py
index fc06d9e..f625950 100644
--- a/tests/test_all.py
+++ b/tests/test_all.py
@@ -48,12 +48,12 @@ def get_token_pkce(port):
     challenge = base64.urlsafe_b64encode(hashlib.sha256(verifier.encode()).digest()).rstrip(b"=").decode()
     r = httpx.get(f"http://127.0.0.1:{port}/authorize", params={
         "response_type": "code", "client_id": "test",
-        "redirect_uri": "http://localhost/cb", "code_challenge": challenge, "code_challenge_method": "S256",
+        "redirect_uri": "https://claude.ai/api/mcp/auth_callback", "code_challenge": challenge, "code_challenge_method": "S256",
     }, follow_redirects=False, timeout=10)
     assert r.status_code == 302
     code = r.headers["location"].split("code=")[1].split("&")[0]
     r2 = httpx.post(f"http://127.0.0.1:{port}/token", data={
-        "grant_type": "authorization_code", "code": code, "client_id": "test", "code_verifier": verifier,
+        "grant_type": "authorization_code", "code": code, "client_id": "test", "client_secret": TEST_SECRET, "code_verifier": verifier,
     }, timeout=10)
     assert r2.status_code == 200
     return r2.json()["access_token"]