Smarty Security Policy

From WHMCS Documentation

We added this feature in WHMCS 7.0.

Smarty Security Policies are security hardening measures that protect a system.

System and Mail Policies

WHMCS applies a Smarty Security Policy for system-wide use and a mail policy for stored and dynamic email-based templates.

The System Policy

The system policy does not restrict PHP beyond the version-specific behaviors in the sections below.

The Mail Policy

The mail policy restricts the use of variable modifiers in email-based templates. Additionally, the policy will not allow any calls to static classes, fetching any data from PHP streams, or accessing any super global variables.

By default, the mail policy:

  • Allows the following variable modifiers:
    • escape
    • count
    • urlencode
    • ucfirst
    • date_format
  • Restricts the use of native PHP functions to:
    • isset
    • empty
    • count
    • sizeof
    • in_array
    • is_array
    • time
    • nl2br
  • Blocks the following Smarty tags:
    • block
    • function
    • include

Version-Specific Smarty Tag Support

In WHMCS 9.0, we plan to remove all backwards compatibility for legacy Smarty {php}, {include_php}, and {insert} tags. This will also remove the related Allow Smarty PHP Tags setting in the Security tab at Configuration () > System Settings > General Settings, or, prior to WHMCS 8.0, Setup > General Settings.

  • WHMCS 8.7 introduced reports and warnings to help admins find and eliminate these tags in their custom themes and templates.
  • For more information, see Eliminating Legacy Smarty Tags.

Allow Smarty PHP Tags

In WHMCS 8.7 and earlier, WHMCS honors the Allow Smarty PHP Tags setting in the Security tab at Configuration () > System Settings > General Settings, or, prior to WHMCS 8.0, Setup > General Settings.

  • All template files that use the system policy are file-based (for example, system themes and order form templates) and require file-level access. Because of this, they are automatically implicitly trusted.
  • Custom system themes are much more likely to have additional PHP-oriented logic, and so any restrictions on them from WHMCS could result in website rendering issues. It is completely within your discretion to determine whether implicit trust at the file level is invalid. You may make any appropriate restrictions for this system policy.

{include_php} Tag Use

In WHMCS 8.7 and earlier, you can use the deprecated {include_php} syntax. To do this, you must whitelist the full path to the script's directory in the trusted_dir setting for your policy:

// System policy:
$smarty_security_policy = [
'system' => [
'trusted_dir' => [

For a list of possible settings and their behavior with arrays and Boolean values, see Smarty documentation.

Redefining Security Policies in WHMCS 8.7 and Earlier

If you want to redefine either the system or mail policies, add a $smarty_security_policy setting to the configuration.php file.

The example below limits email templates by modifying the mail policy to only allow the native ucwords PHP function. It does not change the default restrictions on variable modifiers:

// Smarty custom email based template policy:
$smarty_security_policy = [
'mail' => [
'php_functions' => [

The example below restricts the use of variable modifiers to only permit the strpos variable modifier in an email template without changing the default restrictions on PHP functions:

// Smarty custom email based template policy:
$smarty_security_policy = [
'mail' => [
'php_modifiers' => [

Supported Policy Settings and Values

The settings that a WHMCS Smarty Security Policy enforces are the same as the settings that the Smarty library itself defines. For more information, see the Smarty documentation.

In WHMCS 8.0 and later, to improve security, WHMCS doesn't honor Smarty's disabled_special_smarty_vars parameter. Instead, policies should use the enabled_special_smarty_vars parameter. This change in behaviour is an "only allow" paradigm to the most sensitive parts of the Smarty engine implementation.

// Smarty enable special variables policy:
$smarty_security_policy = [
'system' => [
'enabled_special_smarty_vars' => [

The enabled_special_smarty_vars value must be an array using Smarty's options. The WHMCS system policy enables the following values for compatibility with older templates, but your current or future WHMCS templates may not require them:


Defining your own Smarty Security Policy requires you to include all of the variables that client and admin templates use, including the ones that WHMCS otherwise enables by default (as above).