Vulnerability · Published Mar 30, 2026 · Assigned by Wordfence
CVE-2026-4257Contact Form by Supsystic <= 1.7.36 - Unauthenticated Server-Side Template Injection via Prefill Functionality
Critical 9.8
In plain English
A critical-severity code injection in Contact Form by Supsystic from supsysticcom. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 41.5% (higher than 99% of all known vulnerabilities). Ready-made attack tooling exists: Metasploit, Nuclei, public proof-of-concept code.
Official description
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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| supsysticcom | Contact Form by Supsystic | 0 – through 1.7.36 |
Weakness: CWE-94 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H