Solspace Freeform: Limited Twig template injection via submitted field values

Summary

A limited server-side Twig template injection issue was identified in Solspace Freeform for Craft CMS. In affected versions, submitted form field values could be evaluated as Twig in certain rendering contexts.

Unauthenticated users could submit Twig expressions through public Freeform forms and have those expressions evaluated when the submitted values were rendered back into the form response. Confirmed impact includes disclosure of limited server/environment information, such as the PHP version and absolute filesystem paths.

No evidence was found that this issue allowed access to Craft globals, environment variables, database credentials, mailer credentials, security keys, or remote code execution in the tested environment.

Details

Plugin: Solspace Freeform Affected versions: Freeform 5.0.0 through 5.10.13 CMS: Craft CMS Authentication required: None Attack vector: Public Freeform form submission

Submitted field values were passed through Freeform’s isolated Twig renderer. As a result, Twig expressions included in submitted values could be evaluated server-side and reflected in the HTTP response.

The isolated Twig context appears to limit the available functions and globals. Confirmed accessible values were limited to PHP/core constants and Craft bootstrap constants such as:

{{ constant('PHP_VERSION') }}
{{ constant('PHP_OS') }}
{{ constant('CRAFT_BASE_PATH') }}
{{ constant('CRAFT_VENDOR_PATH') }}

Testing did not confirm access to:

craft
craft.app
alias()
getenv()
database credentials
mailer credentials
Craft security key
Craft license key
environment variables

Proof of Concept

1. Submit a public Freeform form.

2. Inject the following payload into an email field:

{{ constant('PHP_VERSION') }}@example.com

The response may reflect the evaluated PHP version, for example:

value="[email protected]"

3. Inject the following payload into a text field:

{{ constant('CRAFT_VENDOR_PATH') }}

The response may reflect the absolute vendor path, for example:

/var/www/example-site/production/vendor/

Impact

An unauthenticated attacker with access to a public Freeform form could cause limited Twig expressions to be evaluated server-side.