diff --git a/cms/server/admin/handlers/main.py b/cms/server/admin/handlers/main.py
index e3ce0760aa..4557e28a0b 100644
--- a/cms/server/admin/handlers/main.py
+++ b/cms/server/admin/handlers/main.py
@@ -31,6 +31,7 @@
 from cms import ServiceCoord, get_service_shards, get_service_address
 from cms.db import Admin, Contest, Question
 from cms.server.jinja2_toolbox import markdown_filter
+from cms.server.util import normalize_login_next_page
 from cmscommon.crypto import validate_password
 from cmscommon.datetime import make_datetime, make_timestamp
 from .base import BaseHandler, SimpleHandler, require_permission
@@ -48,12 +49,7 @@ def post(self):
         next_page: str = self.get_argument("next", None)
         if next_page is not None:
             error_args["next"] = next_page
-            if next_page != "/":
-                next_page = self.url(*next_page.strip("/").split("/"))
-            else:
-                next_page = self.url()
-        else:
-            next_page = self.url()
+        next_page = normalize_login_next_page(next_page, self.url, self.url())
         error_page = self.url("login", **error_args)
 
         username: str = self.get_argument("username", "")
diff --git a/cms/server/contest/handlers/main.py b/cms/server/contest/handlers/main.py
index 93402e2b0c..2b3e60f160 100644
--- a/cms/server/contest/handlers/main.py
+++ b/cms/server/contest/handlers/main.py
@@ -52,6 +52,7 @@
 from cms.grading.languagemanager import get_language
 from cms.grading.steps import COMPILATION_MESSAGES, EVALUATION_MESSAGES
 from cms.server import multi_contest
+from cms.server.util import normalize_login_next_page
 from cms.server.contest.authentication import validate_login
 from cms.server.contest.communication import get_communications
 from cmscommon.crypto import hash_password, validate_password
@@ -217,12 +218,7 @@ def post(self):
         next_page: str | None = self.get_argument("next", None)
         if next_page is not None:
             error_args["next"] = next_page
-            if next_page != "/":
-                next_page = self.url(*next_page.strip("/").split("/"))
-            else:
-                next_page = self.url()
-        else:
-            next_page = self.contest_url()
+        next_page = normalize_login_next_page(next_page, self.url, self.contest_url())
         error_page = self.contest_url(**error_args)
 
         username: str = self.get_argument("username", "")
diff --git a/cms/server/util.py b/cms/server/util.py
index 3251a1fc24..902e521352 100644
--- a/cms/server/util.py
+++ b/cms/server/util.py
@@ -28,7 +28,7 @@
 
 import logging
 from functools import wraps
-from urllib.parse import quote, urlencode
+from urllib.parse import quote, urlencode, urlsplit
 
 import collections
 try:
@@ -168,6 +168,38 @@ def __getitem__(self, component: object) -> typing.Self:
         return self.__class__(self.__call__(component))
 
 
+def normalize_login_next_page(next_page: str | None, url: Url, default_url: str) -> str:
+    """Normalize a login redirection target.
+
+    Accept only local absolute-path targets (plus optional query), and
+    rebase them through the provided URL builder. Query-only values are
+    treated as "/" and preserved.
+
+    next_page: raw value of the "next" parameter.
+    url: URL builder for local paths.
+    default_url: fallback when next_page is missing or invalid.
+
+    return: normalized redirect target.
+    """
+    if next_page is None:
+        return default_url
+
+    split = urlsplit(next_page)
+    path = split.path or "/"
+    if split.scheme or split.netloc or not path.startswith("/"):
+        return default_url
+
+    if path != "/":
+        normalized = url(*path.strip("/").split("/"))
+    else:
+        normalized = url()
+
+    if split.query:
+        normalized += "?" + split.query
+
+    return normalized
+
+
 class CommonRequestHandler(RequestHandler):
     """Encapsulates shared RequestHandler functionality.