Cracklib patch for the Roundcube/password plugin.
Thanks to Tony Fung https://notes.sagredo.eu/en/qmail-notes-185/roundcube-plugins-35.html#comment1651

Use like this

cd /var/www/roundcube
wget https://notes.sagredo.eu/files/qmail/patches/roundcube/cracklib-roundcube_pwd_plugin.patch
patch -p1 < cracklib-roundcube_pwd_plugin.patch

More info here https://notes.sagredo.eu/en/qmail-notes-185/roundcube-plugins-35.html#password

=============================================================================================================

diff -ruN roundcube-original/plugins/password/drivers/sql.php roundcube/plugins/password/drivers/sql.php
--- roundcube-original/plugins/password/drivers/sql.php	2021-12-29 23:29:23.000000000 +0100
+++ roundcube/plugins/password/drivers/sql.php	2022-08-08 11:14:29.753978628 +0200
@@ -26,6 +26,21 @@
 class rcube_sql_password
 {
     /**
+     * Finds the cracklib-check path
+     *
+     * @return string Result
+     */
+    function get_cracklib_path()
+    {
+        $paths = array('/sbin/cracklib-check', '/usr/sbin/cracklib-check', '/usr/local/sbin/cracklib-check');
+        foreach ($paths as $path)
+        {
+            if (file_exists($path))	break;
+        }
+        return $path;
+    }
+
+    /**
      * Update current user password
      *
      * @param string $curpass Current password
@@ -36,6 +51,15 @@
     function save($curpass, $passwd)
     {
         $rcmail = rcmail::get_instance();
+        exec("echo ".$passwd." | ".$this->get_cracklib_path()." 2>/dev/null", $output, $return_var);
+
+        if(preg_match("/^.*\: ([^:]+)$/", $output[0], $matches)) {
+            // Check response:
+            if(strtoupper($matches[1])!=="OK") {
+                // Cracklib doesn't like it:
+                return PASSWORD_CONSTRAINT_VIOLATION;
+            }
+        }
 
         if (!($sql = $rcmail->config->get('password_query'))) {
             $sql = 'SELECT update_passwd(%c, %u)';
diff -ruN roundcube-original/plugins/password/drivers/vpopmaild.php roundcube/plugins/password/drivers/vpopmaild.php
--- roundcube-original/plugins/password/drivers/vpopmaild.php	2021-12-29 23:29:23.000000000 +0100
+++ roundcube/plugins/password/drivers/vpopmaild.php	2022-08-08 11:15:15.512921792 +0200
@@ -26,12 +26,36 @@
 
 class rcube_vpopmaild_password
 {
+    /**
+     * Finds the cracklib-check path
+     *
+     * @return string Result
+     */
+    function get_cracklib_path()
+    {
+        $paths = array('/sbin/cracklib-check', '/usr/sbin/cracklib-check', '/usr/local/sbin/cracklib-check');
+        foreach ($paths as $path)
+        {
+            if (file_exists($path)) break;
+        }
+        return $path;
+    }
+
     function save($curpass, $passwd, $username)
     {
         $rcmail    = rcmail::get_instance();
         $vpopmaild = new Net_Socket();
         $host      = $rcmail->config->get('password_vpopmaild_host');
         $port      = $rcmail->config->get('password_vpopmaild_port');
+        exec("echo ".$passwd." | ".$this->get_cracklib_path()." 2>/dev/null", $output, $return_var);
+
+        if(preg_match("/^.*\: ([^:]+)$/", $output[0], $matches)) {
+            // Check response:
+            if(strtoupper($matches[1])!=="OK") {
+                // Cracklib doesn't like it:
+                return PASSWORD_CONSTRAINT_VIOLATION;
+            }
+        }
 
         $result = $vpopmaild->connect($host, $port, null);
         if (is_a($result, 'PEAR_Error')) {