The Contact Form by Supsystic plugin for WordPress is vulnerable to Server-Side Template Injection (SSTI) leading to Remote Code Execution (RCE) in all versions up to, and including, 1.7.36. This is due to the plugin using the Twig `Twig_Loader_String` template engine without sandboxing, combined with the `cfsPreFill` prefill functionality that allows unauthenticated users to inject arbitrary Twig expressions into form field values via GET parameters. This makes it possible for unauthenticated attackers to execute arbitrary PHP functions and OS commands on the server by leveraging Twig's `registerUndefinedFilterCallback()` method to register arbitrary PHP callbacks.
CVE-2026-4257 is a critical severity with CVSS 9.8 Remote Code Execution issue affecting the Plugin Contact Form by Supsystic. It affects Versions up to 1.7.36 and is fixed in 1.8.0.
CVE-2026-4257 is tracked for the Plugin Contact Form by Supsystic as critical severity with CVSS 9.8. The affected range is Versions up to 1.7.36. Update Contact Form by Supsystic to 1.8.0 or newer where that version is compatible with the site.
| Software Type | Plugin |
|---|---|
| Software Slug |
contact-form-by-supsystic
View on wordpress.org
|
| CVE | CVE-2026-4257 |
| Patched Versions |
1.8.0
|
| Affected Versions |
Versions up to 1.7.36
|
These internal links group the same WordPress plugin by CVE, issue type, severity, and patch status so operators and search engines can connect the full vulnerability cluster.
Contact Form by Supsystic <= 1.7.28 - Authenticated (Admin+) Remote Code Execution
Contact Form by Supsystic <= 1.7.36 - Reflected Cross-Site Scripting
Contact Form by Supsystic <= 1.7.29 - Cross-Site Request Forgery to Stored Cross-Site Scripting via saveAsCopy AJAX Action
Contact Form by Supsystic <= 1.7.14 - Reflected Cross-Site scripting
Contact Form by Supsystic <= 1.7.24 - Cross-Site Request Forgery via AJAX action
Contact Form by Supsystic <= 1.7.28 - Authenticated (Administrator+) Stored Cross-Site Scripting
Contact Form by Supsystic <= 1.7.27 - Cross-Site Request Forgery
Contact Form by Supsystic <= 1.7.10 - SQL Injections
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