Index: plugins/password/password.php
--- plugins/password/password.php.orig
+++ plugins/password/password.php
@@ -583,7 +583,7 @@ 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}';
