diff --git a/lam/help/help.inc b/lam/help/help.inc
index 82e8a417..9cd82dd9 100644
--- a/lam/help/help.inc
+++ b/lam/help/help.inc
@@ -171,6 +171,8 @@ $helpArray = array (
 					"Text" => _('Specifies if the password must not contain the user name.')),
 				"248" => array ("Headline" => _('Password must not contain part of user/first/last name'),
 					"Text" => _('Specifies if the password must not contain 3 or more characters of the user/first/last name.')),
+				"249" => array ("Headline" => _('External password check'),
+					"Text" => _('Please specify the URL (e.g. "https://api.pwnedpasswords.com/range/{SHA1PREFIX}") of your external password check and the severity if the check fails.')),
 				"250" => array ("Headline" => _("Filter"),
 					"Text" => _("Here you can input simple filter expressions (e.g. 'value' or 'v*'). The filter is case-sensitive.")),
 				"260" => array ("Headline" => _("Additional LDAP filter"),
diff --git a/lam/lib/config.inc b/lam/lib/config.inc
index eae0c1bd..af7b8697 100644
--- a/lam/lib/config.inc
+++ b/lam/lib/config.inc
@@ -1,10 +1,9 @@
 <?php
 use \LAM\LIB\TWO_FACTOR\TwoFactorProviderService;
 /*
-$Id$
 
   This code is part of LDAP Account Manager (http://www.ldap-account-manager.org/)
-  Copyright (C) 2003 - 2017  Roland Gruber
+  Copyright (C) 2003 - 2018  Roland Gruber
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -2287,6 +2286,9 @@ class LAMCfgMain {
 	/** password may contain more than 2 characters of user/first/last name */
 	public $passwordMustNotContain3Chars = 'false';
 
+	/** external URL for password checking (e.g. https://domain.com/url/{SHA1}) */
+	public $externalPwdCheckUrl = null;
+
 	/** path to config file */
 	private $conffile;
 
@@ -2311,6 +2313,7 @@ class LAMCfgMain {
 		"passwordMinUpper", "passwordMinLower", "passwordMinNumeric",
 		"passwordMinClasses", "passwordMinSymbol", 'checkedRulesCount',
 		'passwordMustNotContainUser', 'passwordMustNotContain3Chars',
+		'externalPwdCheckUrl',
 		"mailEOL", 'errorReporting', 'encryptSession', 'allowedHostsSelfService',
 		'license'
 	);
@@ -2405,6 +2408,7 @@ class LAMCfgMain {
 		if (!in_array("checkedRulesCount", $saved)) array_push($file_array, "\n\n# Password: checked rules\n" . "checkedRulesCount: " . $this->checkedRulesCount);
 		if (!in_array("passwordMustNotContain3Chars", $saved)) array_push($file_array, "\n\n# Password: must not contain part of user name\n" . "passwordMustNotContain3Chars: " . $this->passwordMustNotContain3Chars);
 		if (!in_array("passwordMustNotContainUser", $saved)) array_push($file_array, "\n\n# Password: must not contain user name\n" . "passwordMustNotContainUser: " . $this->passwordMustNotContainUser);
+		if (!in_array("externalPwdCheckUrl", $saved)) array_push($file_array, "\n\n" . "externalPwdCheckUrl: " . $this->externalPwdCheckUrl);
 		if (!in_array("mailEOL", $saved)) array_push($file_array, "\n\n# Email format (default/unix)\n" . "mailEOL: " . $this->mailEOL);
 		if (!in_array("errorReporting", $saved)) array_push($file_array, "\n\n# PHP error reporting (default/system)\n" . "errorReporting: " . $this->errorReporting);
 		if (!in_array("license", $saved)) array_push($file_array, "\n\n# License\n" . "license: " . $this->license);
diff --git a/lam/lib/security.inc b/lam/lib/security.inc
index b014cd07..bea11c4d 100644
--- a/lam/lib/security.inc
+++ b/lam/lib/security.inc
@@ -491,6 +491,49 @@ function checkPasswordStrength($password, $userName, $otherUserAttrs) {
 			}
 		}
 	}
+	// check external password service
+	if (!checkPwdWithExternalPasswordService($cfg, $password)) {
+		return _('Your selected password is known to be insecure.');
+	}
+	return true;
+}
+
+/**
+ * Checks the password against the external password service.
+ *
+ * @param LAMCfgMain $cfg main configuration
+ * @param string $password password
+ * @return boolean password accepted as secure
+ */
+function checkPwdWithExternalPasswordService($cfg, $password) {
+	if (!function_exists('curl_init') || empty($cfg->externalPwdCheckUrl)) {
+		return true;
+	}
+	$sha1 = sha1($password);
+	$sha1Prefix = substr($sha1, 0, 5);
+	$sha1Suffix = substr($sha1, 5);
+	$curl = curl_init();
+	curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
+	$url = $cfg->externalPwdCheckUrl;
+	$url = str_replace('{SHA1PREFIX}', $sha1Prefix, $url);
+	curl_setopt($curl, CURLOPT_URL, $url);
+	$results = curl_exec($curl);
+	$code = curl_errno($curl);
+	if ($code) {
+		logNewMessage(LOG_ERR, 'Error calling the external password service at ' . $url
+			. '. ' . curl_error($curl));
+		return true;
+	}
+	curl_close($curl);
+	if (empty($results)) {
+		return true;
+	}
+	$results = explode("\n", $results);
+	foreach ($results as $result) {
+		if (stripos($result, $sha1Suffix . ':') !== false) {
+			return false;
+		}
+	}
 	return true;
 }
 
diff --git a/lam/templates/config/mainmanage.php b/lam/templates/config/mainmanage.php
index cd8d9a42..450f8202 100644
--- a/lam/templates/config/mainmanage.php
+++ b/lam/templates/config/mainmanage.php
@@ -179,6 +179,12 @@ if (isset($_POST['submitFormData'])) {
 	$cfg->checkedRulesCount = $_POST['passwordRulesCount'];
 	$cfg->passwordMustNotContain3Chars = isset($_POST['passwordMustNotContain3Chars']) && ($_POST['passwordMustNotContain3Chars'] == 'on') ? 'true' : 'false';
 	$cfg->passwordMustNotContainUser = isset($_POST['passwordMustNotContainUser']) && ($_POST['passwordMustNotContainUser'] == 'on') ? 'true' : 'false';
+	if (function_exists('curl_init')) {
+		$cfg->externalPwdCheckUrl = $_POST['externalPwdCheckUrl'];
+		if (!empty($cfg->externalPwdCheckUrl) && (strpos($cfg->externalPwdCheckUrl, '{SHA1PREFIX}') === false)) {
+			$errors[] = _('The URL for the external password check is invalid.');
+		}
+	}
 	if (isset($_POST['sslCaCertUpload'])) {
 		if (!isset($_FILES['sslCaCert']) || ($_FILES['sslCaCert']['size'] == 0)) {
 			$errors[] = _('No file selected.');
@@ -378,6 +384,10 @@ $passwordMustNotContainUser = ($cfg->passwordMustNotContainUser === 'true') ? tr
 $row->add(new htmlResponsiveInputCheckbox('passwordMustNotContainUser',$passwordMustNotContainUser , _('Password must not contain user name'), '247'), 12);
 $passwordMustNotContain3Chars = ($cfg->passwordMustNotContain3Chars === 'true') ? true : false;
 $row->add(new htmlResponsiveInputCheckbox('passwordMustNotContain3Chars', $passwordMustNotContain3Chars, _('Password must not contain part of user/first/last name'), '248'), 12);
+if (function_exists('curl_init')) {
+	$row->addVerticalSpacer('1rem');
+	$row->add(new htmlResponsiveInputField(_('External password check'), 'externalPwdCheckUrl', $cfg->externalPwdCheckUrl, '249'), 12);
+}
 
 // logging
 $row->add(new htmlSubTitle(_("Logging")), 12);