🔒 Make session handling more secure

* 🔒️ Tie remember_me cookie to password hash

That way when the password gets changed,
existing cookies automatically get
invalidated.

* 🔒️ Invalidate user sessions on password change

This will require a user to log in again after
their password is changed, either by themselves
or through an admin.

This is a slight change in behaviour compared
to before, but makes sure password changes
are enforced across all existing sessions.

* ♻️ remember_key_for_user => signature_key_for_user

* 🔒️ Invalidate sessions after 15min of inactivity

The server has been keeping track of login
session for a while, but now it also only
considers such (active login) sessions fresh
that have been active within the past 15min.

That way, a session cookie's lifetime is now
also restricted server side. An active
socket connection suffices to keep the
session alive, as do any other requests
using the cookie.

As the session tracking happens in-memory,
all sessions will become invalid on server
restart. However, if the remember me cookie
is set, after server restart a passive
login will succeed.

* 🔒️ Limit remember_me validity to 90 days

So far that was only done through the cookie
duration, and with a year to boot. Now we
encode the creation date into the cookie
and check against that, if it exceeds the
cookie duration the cookie is considered
unset.

Will prevent reuse of ancient remember me
cookies (and force the user to login at
least once every 90d).

* 💚 Fix unit tests

New cookie handling requires a faked flask
config object.

Related: https://huntr.dev/bounties/d27d232b-2578-4b32-b3b4-74aabdadf629/

src/octoprint/access/users.py

@@ -127,11 +127,9 @@ def _cleanup_sessions(self):
         for session, user in list(self._session_users_by_session.items()):
             if not isinstance(user, SessionUser):
                 continue
-            if user.created + (24 * 60 * 60) < time.monotonic():
+            if user.touched + (15 * 60) < time.monotonic():
                 self._logger.info(
-                    "Cleaning up user session {} for user {}".format(
-                        session, user.get_id()
-                    )
+                    f"Cleaning up user session {session} for user {user.get_id()}"
                 )
                 self.logout_user(user, stale=True)
 
@@ -176,6 +174,9 @@ def check_password(self, username, password):
                 # old hash doesn't match either, wrong password
                 return False
 
+    def signature_key_for_user(self, username, salt=None):
+        return self.create_password_hash(username, salt=salt)
+
     def add_user(self, username, password, active, permissions, groups, overwrite=False):
         pass
 
@@ -227,29 +228,38 @@ def remove_user(self, username):
             del self._sessionids_by_userid[username]
 
     def validate_user_session(self, userid, session):
+        self._cleanup_sessions()
+
         if session in self._session_users_by_session:
             user = self._session_users_by_session[session]
             return userid == user.get_id()
 
         return False
 
-    def find_user(self, userid=None, session=None):
+    def find_user(self, userid=None, session=None, fresh=False):
+        self._cleanup_sessions()
+
         if session is not None and session in self._session_users_by_session:
             user = self._session_users_by_session[session]
             if userid is None or userid == user.get_id():
+                user.touch()
                 return user
 
         return None
 
     def find_sessions_for(self, matcher):
+        self._cleanup_sessions()
+
         result = []
         for user in self.get_all_users():
             if matcher(user):
                 try:
                     session_ids = self._sessionids_by_userid[user.get_id()]
                     for session_id in session_ids:
                         try:
-                            result.append(self._session_users_by_session[session_id])
+                            session_user = self._session_users_by_session[session_id]
+                            session_user.touch()
+                            result.append(session_user)
                         except KeyError:
                             # unknown session after all
                             continue
@@ -780,6 +790,14 @@ def change_user_password(self, username, password):
             self._dirty = True
             self._save()
 
+            self._trigger_on_user_modified(user)
+
+    def signature_key_for_user(self, username, salt=None):
+        if username not in self._users:
+            raise UnknownUser(username)
+        user = self._users[username]
+        return UserManager.create_password_hash(username + user._passwordHash, salt=salt)
+
     def change_user_setting(self, username, key, value):
         if username not in self._users:
             raise UnknownUser(username)
@@ -845,10 +863,10 @@ def remove_user(self, username):
         self._dirty = True
         self._save()
 
-    def find_user(self, userid=None, apikey=None, session=None):
+    def find_user(self, userid=None, apikey=None, session=None, fresh=False):
         user = UserManager.find_user(self, userid=userid, session=session)
 
-        if user is not None:
+        if user is not None or (session and fresh):
             return user
 
         if userid is not None:
@@ -1383,8 +1401,7 @@ def __init__(self, user):
         wrapt.ObjectProxy.__init__(self, user)
 
         self._self_session = "".join("%02X" % z for z in bytes(uuid.uuid4().bytes))
-        self._self_created = time.monotonic()
-        self._self_touched = time.monotonic()
+        self._self_created = self._self_touched = time.monotonic()
 
     @property
     def session(self):

src/octoprint/server/__init__.py

@@ -130,7 +130,7 @@
     loginFromApiKeyRequestHandler,
     requireLoginRequestHandler,
 )
-from octoprint.server.util.flask import PreemptiveCache
+from octoprint.server.util.flask import PreemptiveCache, validate_session_signature
 from octoprint.settings import settings
 
 VERSION = __version__
@@ -187,12 +187,25 @@ def load_user(id):
     else:
         sessionid = None
 
+    if session and "usersession.signature" in session:
+        sessionsig = session["usersession.signature"]
+    else:
+        sessionsig = ""
+
     if sessionid:
-        user = userManager.find_user(userid=id, session=sessionid)
+        # session["_fresh"] is False if the session comes from a remember me cookie,
+        # True if it came from a use of the login dialog
+        user = userManager.find_user(
+            userid=id, session=sessionid, fresh=session.get("_fresh", False)
+        )
     else:
         user = userManager.find_user(userid=id)
 
-    if user and user.is_active:
+    if (
+        user
+        and user.is_active
+        and (not sessionid or validate_session_signature(sessionsig, id, sessionid))
+    ):
         return user
 
     return None
@@ -1366,7 +1379,9 @@ def _setup_app(self, app):
 
         app.config["TEMPLATES_AUTO_RELOAD"] = True
         app.config["JSONIFY_PRETTYPRINT_REGULAR"] = False
+        app.config["REMEMBER_COOKIE_DURATION"] = 90 * 24 * 60 * 60  # 90 days
         app.config["REMEMBER_COOKIE_HTTPONLY"] = True
+        # REMEMBER_COOKIE_SECURE will be taken care of by our custom cookie handling
 
         # we must not set this before TEMPLATES_AUTO_RELOAD is set to True or that won't take
         app.debug = self._debug

src/octoprint/server/api/__init__.py

@@ -38,6 +38,7 @@
     limit,
     no_firstrun_access,
     passive_login,
+    session_signature,
 )
 from octoprint.settings import settings as s
 from octoprint.settings import valid_boolean_trues
@@ -312,6 +313,9 @@ def login():
 
                 user = octoprint.server.userManager.login_user(user)
                 session["usersession.id"] = user.session
+                session["usersession.signature"] = session_signature(
+                    username, user.session
+                )
                 g.user = user
 
                 login_user(user, remember=remember)

src/octoprint/server/util/flask.py

@@ -5,11 +5,13 @@
 __copyright__ = "Copyright (C) 2014 The OctoPrint Project - Released under terms of the AGPLv3 License"
 
 import functools
+import hashlib
+import hmac
 import logging
 import os
 import threading
 import time
-from datetime import datetime
+from datetime import datetime, timedelta
 from typing import Union
 
 import flask
@@ -23,6 +25,9 @@
 import webassets.updater
 import webassets.utils
 from cachelib import BaseCache
+from flask import current_app
+from flask_login import COOKIE_NAME as REMEMBER_COOKIE_NAME
+from flask_login.utils import decode_cookie, encode_cookie
 from werkzeug.local import LocalProxy
 from werkzeug.utils import cached_property
 
@@ -422,6 +427,49 @@ def host_to_server_and_port(host, scheme):
 # ~~ request and response versions
 
 
+def encode_remember_me_cookie(value):
+    from octoprint.server import userManager
+
+    name = value.split("|")[0]
+    try:
+        remember_key = userManager.signature_key_for_user(
+            name, salt=current_app.config["SECRET_KEY"]
+        )
+        timestamp = datetime.utcnow().timestamp()
+        return encode_cookie(f"{name}|{timestamp}", key=remember_key)
+    except Exception:
+        pass
+
+    return ""
+
+
+def decode_remember_me_cookie(value):
+    from octoprint.server import userManager
+
+    parts = value.split("|")
+    if len(parts) == 3:
+        name, created, _ = parts
+
+        try:
+            # valid signature?
+            signature_key = userManager.signature_key_for_user(
+                name, salt=current_app.config["SECRET_KEY"]
+            )
+            cookie = decode_cookie(value, key=signature_key)
+            if cookie:
+                # still valid?
+                if (
+                    datetime.fromtimestamp(float(created))
+                    + timedelta(seconds=current_app.config["REMEMBER_COOKIE_DURATION"])
+                    > datetime.utcnow()
+                ):
+                    return encode_cookie(name)
+        except Exception:
+            pass
+
+    raise ValueError("Invalid remember me cookie")
+
+
 class OctoPrintFlaskRequest(flask.Request):
     environment_wrapper = staticmethod(lambda x: x)
 
@@ -437,10 +485,23 @@ def cookies(self):
         result = {}
         desuffixed = {}
         for key, value in cookies.items():
-            if key.endswith(self.cookie_suffix):
-                desuffixed[key[: -len(self.cookie_suffix)]] = value
-            else:
-                result[key] = value
+
+            def process_value(k, v):
+                if k == current_app.config.get(
+                    "REMEMBER_COOKIE_NAME", REMEMBER_COOKIE_NAME
+                ):
+                    return decode_remember_me_cookie(v)
+                return v
+
+            try:
+                if key.endswith(self.cookie_suffix):
+                    key = key[: -len(self.cookie_suffix)]
+                    desuffixed[key] = process_value(key, value)
+                else:
+                    result[key] = process_value(key, value)
+            except ValueError:
+                # ignore broken cookies
+                pass
 
         result.update(desuffixed)
         return result
@@ -471,7 +532,7 @@ def cookie_suffix(self):
 
 
 class OctoPrintFlaskResponse(flask.Response):
-    def set_cookie(self, key, *args, **kwargs):
+    def set_cookie(self, key, value="", *args, **kwargs):
         # restrict cookie path to script root
         kwargs["path"] = flask.request.script_root + kwargs.get("path", "/")
 
@@ -490,9 +551,13 @@ def set_cookie(self, key, *args, **kwargs):
         # set secure if necessary
         kwargs["secure"] = settings().getBoolean(["server", "cookies", "secure"])
 
+        # tie account properties to remember me cookie (e.g. current password hash)
+        if key == current_app.config.get("REMEMBER_COOKIE_NAME", REMEMBER_COOKIE_NAME):
+            value = encode_remember_me_cookie(value)
+
         # add request specific cookie suffix to name
         flask.Response.set_cookie(
-            self, key + flask.request.cookie_suffix, *args, **kwargs
+            self, key + flask.request.cookie_suffix, value=value, *args, **kwargs
         )
 
     def delete_cookie(self, key, path="/", domain=None):
@@ -608,6 +673,9 @@ def login(u):
         )
         if hasattr(u, "session"):
             flask.session["usersession.id"] = u.session
+            flask.session["usersession.signature"] = session_signature(
+                u.get_id(), u.session
+            )
         flask.g.user = u
 
         eventManager().fire(Events.USER_LOGGED_IN, payload={"username": u.get_id()})
@@ -1832,3 +1900,19 @@ def default(self, obj):
             return JsonEncoding.encode(obj)
         except TypeError:
             return flask.json.JSONEncoder.default(self, obj)
+
+
+##~~ Session signing
+
+
+def session_signature(user, session):
+    from octoprint.server import userManager
+
+    key = userManager.signature_key_for_user(user, salt=current_app.config["SECRET_KEY"])
+    return hmac.new(
+        key.encode("utf-8"), session.encode("utf-8"), hashlib.sha512
+    ).hexdigest()
+
+
+def validate_session_signature(sig, user, session):
+    return hmac.compare_digest(sig, session_signature(user, session))

src/octoprint/server/util/sockjs.py

@@ -21,9 +21,10 @@
 import octoprint.vendor.sockjs.tornado.util
 from octoprint.access.groups import GroupChangeListener
 from octoprint.access.permissions import Permissions
-from octoprint.access.users import LoginStatusListener
+from octoprint.access.users import LoginStatusListener, SessionUser
 from octoprint.events import Events
 from octoprint.settings import settings
+from octoprint.util import RepeatedTimer
 from octoprint.util.json import dumps as json_dumps
 from octoprint.util.version import get_python_version_string
 
@@ -173,13 +174,24 @@ def __init__(
         self._subscriptions_active = False
         self._subscriptions = {"state": False, "plugins": [], "events": []}
 
+        self._keep_alive = RepeatedTimer(
+            60, self._keep_alive_callback, condition=lambda: self._authed
+        )
+
     @staticmethod
     def _get_remote_address(info):
         forwarded_for = info.headers.get("X-Forwarded-For")
         if forwarded_for is not None:
             return forwarded_for.split(",")[0]
         return info.ip
 
+    def _keep_alive_callback(self):
+        if not self._authed:
+            return
+        if not isinstance(self._user, SessionUser):
+            return
+        self._user.touch()
+
     def __str__(self):
         if self._remoteAddress:
             return f"{self!r} connected to {self._remoteAddress}"
@@ -716,6 +728,8 @@ def _on_login(self, user):
         )
         self._authed = True
 
+        self._keep_alive.start()
+
         for name, hook in self._authed_hooks.items():
             try:
                 hook(self, self._user)

src/octoprint/static/js/app/viewmodels/usersettings.js

@@ -88,7 +88,7 @@ $(function () {
 
             self.userSettingsDialog.trigger("beforeSave");
 
-            function process() {
+            function saveSettings() {
                 var settings = {
                     interface: {
                         language: self.interface_language()
@@ -110,15 +110,15 @@ $(function () {
                         self.access_currentPassword()
                     )
                     .done(function () {
-                        process();
+                        saveSettings();
                     })
                     .fail(function (xhr) {
                         if (xhr.status === 403) {
                             self.access_currentPasswordMismatch(true);
                         }
                     });
             } else {
-                process();
+                saveSettings();
             }
         };