Require a minimum password length of 12 characters for new passwords

Existing shorter passwords keep working and are still rehashed. The CLI
accepts shorter passwords in debug mode for development.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Makefile

@@ -43,4 +43,4 @@ stop-prod:
 
 setup-prod-initial-login:
 	docker-compose exec max flask add-domain finn.st
-	docker-compose exec max flask reset-admin admin@finn.st admin
+	docker-compose exec max flask reset-admin admin@finn.st admin-initial

max/auth/__init__.py

@@ -1,9 +1,19 @@
-from .hashing import check_password, hash_password  # noqa
+from .hashing import MAX_PASSWORD_BYTES, check_password, hash_password  # noqa
 from .middlewares import AuthMiddleware, no_authentication_required  # noqa
-from .password_policy import validate_password  # noqa
+from .password_policy import (  # noqa
+    MIN_PASSWORD_LENGTH,
+    PASSWORD_MESSAGE_ARGUMENTS,
+    validate_password,
+)
 from .passwords import change_password  # noqa
 from .routes import init_routes
 
 
 def init(app):
     init_routes(app)
+    app.context_processor(
+        lambda: dict(
+            min_password_length=MIN_PASSWORD_LENGTH,
+            max_password_bytes=MAX_PASSWORD_BYTES,
+        )
+    )

max/auth/password_policy.py

@@ -1,13 +1,27 @@
-from .hashing import is_password_too_long
+from .hashing import MAX_PASSWORD_BYTES, is_password_too_long
 
+MIN_PASSWORD_LENGTH = 12
+
+PASSWORD_TOO_SHORT_MESSAGE = (
+    "The password must be at least {min_length} characters long"
+)
 PASSWORD_TOO_LONG_MESSAGE = (
-    "The password must be at most 72 bytes long "
-    "(72 characters, fewer with umlauts or special characters)"
+    "The password must be at most {max_bytes} bytes long "
+    "({max_bytes} characters, fewer with umlauts or special characters)"
+)
+# Fills the placeholders of the messages, e.g. t(error, **PASSWORD_MESSAGE_ARGUMENTS)
+PASSWORD_MESSAGE_ARGUMENTS = dict(
+    min_length=MIN_PASSWORD_LENGTH, max_bytes=MAX_PASSWORD_BYTES
 )
 
 
-def validate_password(password: str):
-    """Returns the (untranslated) error message, or None if the password is valid"""
+def validate_password(password: str, min_length=MIN_PASSWORD_LENGTH):
+    """
+    Checks a new password. Returns the (untranslated) error message, or None if the
+    password is valid. Existing passwords are not checked against this policy.
+    """
+    if len(password) < min_length:
+        return PASSWORD_TOO_SHORT_MESSAGE
     if is_password_too_long(password):
         return PASSWORD_TOO_LONG_MESSAGE
     return None

max/auth/passwords.py

@@ -4,7 +4,6 @@ from max.db import update_user
 from max.sessions import session_storage
 
 from .hashing import hash_password, needs_rehash
-from .password_policy import validate_password
 
 
 def change_password(user, password):
@@ -23,11 +22,7 @@ def rehash_password_if_needed(user, password):
     """Replaces an outdated hash, the plain password is only known at the login"""
     if not needs_rehash(user.passwordhash):
         return
-    error = validate_password(password)
-    if error:
-        current_app.logger.warning(
-            'Cannot rehash the password of user %s: "%s"', user.id, error
-        )
-        return
+    # check_password accepted the password, so hash_password can hash it. The policy for
+    # new passwords does not apply here.
     update_user(user.id, passwordhash=hash_password(password))
     current_app.logger.info("Rehashed the password of user %s", user.id)

max/cli.py

@@ -1,6 +1,8 @@
 import click
+from flask import current_app
 
 from .auth import (
+    PASSWORD_MESSAGE_ARGUMENTS,
     check_password as auth_check_password,
     hash_password,
     validate_password,
@@ -22,9 +24,13 @@ def register_cli(app):
 
 
 def abort_if_password_invalid(password):
+    if current_app.debug:
+        # Short passwords like "admin" are fine for development
+        error = validate_password(password, min_length=0)
+    else:
         error = validate_password(password)
     if error:
-        raise click.ClickException(error)
+        raise click.ClickException(error.format(**PASSWORD_MESSAGE_ARGUMENTS))
 
 
 @click.argument("email")

max/exceptions.py

@@ -23,7 +23,8 @@ class PermissionDenied(MaxException):
 
 class InvalidPassword(MaxException):
     """
-    Callers must check the password with validate_password before hashing it.
+    The password is too long for bcrypt. Callers must check new passwords with
+    validate_password before hashing them.
     """
 
 

max/private_static/i18n/de.json

@@ -50,7 +50,8 @@
     "Note changed successfully!": "Notiz wurde erfolgreich bearbeitet!",
     "Both passwords must be given": "Beide Passwörter müssen angegeben werden",
     "Both passwords must be the same": "Beide Passwörter müssen übereinstimmen",
-    "The password must be at most 72 bytes long (72 characters, fewer with umlauts or special characters)": "Das Passwort darf höchstens 72 Bytes lang sein (72 Zeichen, mit Umlauten oder Sonderzeichen weniger)",
+    "The password must be at least {min_length} characters long": "Das Passwort muss mindestens {min_length} Zeichen lang sein",
+    "The password must be at most {max_bytes} bytes long ({max_bytes} characters, fewer with umlauts or special characters)": "Das Passwort darf höchstens {max_bytes} Bytes lang sein ({max_bytes} Zeichen, mit Umlauten oder Sonderzeichen weniger)",
     "Current password": "Aktuelles Passwort",
     "The current password must be given": "Das aktuelle Passwort muss angegeben werden",
     "The current password is wrong": "Das aktuelle Passwort ist falsch",

max/routes/user/change_password.py

@@ -1,6 +1,11 @@
 from flask import flash
 
-from max.auth import change_password, check_password, validate_password
+from max.auth import (
+    PASSWORD_MESSAGE_ARGUMENTS,
+    change_password,
+    check_password,
+    validate_password,
+)
 from max.permissions import AllowAdminOrSelf
 from max.translations import t
 
@@ -47,7 +52,7 @@ class UserChangePassword(AllowAdminOrSelf, BackToUsersMixin, FetchUserTemplateGe
 
         password_error = validate_password(pw1)
         if password_error:
-            flash(t(password_error), category="error")
+            flash(t(password_error, **PASSWORD_MESSAGE_ARGUMENTS), category="error")
             return
 
         change_password(self.user, pw1)

max/routes/user/create.py

@@ -1,6 +1,6 @@
 from flask import flash, url_for
 
-from max.auth import hash_password, validate_password
+from max.auth import PASSWORD_MESSAGE_ARGUMENTS, hash_password, validate_password
 from max.db import EmailAlreadyExists, create_user, get_domains
 from max.permissions import AllowAdmin
 from max.translations import t
@@ -50,7 +50,7 @@ class UserCreate(AllowAdmin, CheckEmailMixin, BaseTemplateGetView):
         else:
             password_error = validate_password(pw1)
             if password_error:
-                flash(t(password_error), category="error")
+                flash(t(password_error, **PASSWORD_MESSAGE_ARGUMENTS), category="error")
                 error = True
             else:
                 self.password = pw1

max/templates/user/change-password.html

@@ -14,12 +14,12 @@
         {% endif %}
         <div class="pure-control-group">
             <label for="password1">{{ t("Password") }}</label>
-            <input id="password1" type="password" name="password1" autocomplete="new-password" maxlength="72" placeholder="{{ t("New password") }}">
+            <input id="password1" type="password" name="password1" autocomplete="new-password" minlength="{{ min_password_length }}" maxlength="{{ max_password_bytes }}" placeholder="{{ t("New password") }}">
         </div>
 
         <div class="pure-control-group">
             <label for="password2">{{ t("Re-enter password") }}</label>
-            <input id="password2" type="password" name="password2" autocomplete="new-password" maxlength="72" placeholder="{{ t("New password") }}">
+            <input id="password2" type="password" name="password2" autocomplete="new-password" minlength="{{ min_password_length }}" maxlength="{{ max_password_bytes }}" placeholder="{{ t("New password") }}">
         </div>
 
         <div class="pure-controls">

max/templates/user/create.html

@@ -19,12 +19,12 @@
 
         <div class="pure-control-group">
             <label for="password1">{{ t("Password") }}</label>
-            <input id="password1" type="password" name="password1" autocomplete="new-password" maxlength="72" placeholder="{{ t("Password") }}">
+            <input id="password1" type="password" name="password1" autocomplete="new-password" minlength="{{ min_password_length }}" maxlength="{{ max_password_bytes }}" placeholder="{{ t("Password") }}">
         </div>
 
         <div class="pure-control-group">
             <label for="password2">{{ t("Re-enter password") }}</label>
-            <input id="password2" type="password" name="password2" autocomplete="new-password" maxlength="72" placeholder="{{ t("Re-enter password") }}">
+            <input id="password2" type="password" name="password2" autocomplete="new-password" minlength="{{ min_password_length }}" maxlength="{{ max_password_bytes }}" placeholder="{{ t("Re-enter password") }}">
         </div>
 
         <div class="pure-controls checkbox">