Index: plugins/password/password.php
--- plugins/password/password.php.orig
+++ plugins/password/password.php
@@ -567,7 +567,7 @@ class password extends rcube_plugin
             case 'blowfish-crypt':
                 $cost = (int) ($options['cost'] ?? $rcmail->config->get('password_blowfish_cost'));
                 $cost = $cost < 4 || $cost > 31 ? 12 : $cost;
-                $prefix = sprintf('$2y$%02d$', $cost);
+                $prefix = sprintf('$2b$%02d$', $cost);
 
                 $crypted = crypt($password, $prefix . rcube_utils::random_bytes(22));
                 $prefix = '{BLF-CRYPT}';
