CVE-2026-4257 Contact Form by Supsystic <= 1.7.36 - Unauthenticated Server-Side Template Injection via Prefill Functionality
Unauthenticated attackers can execute arbitrary code via Server-Side Template Injection in the Contact Form by Supsystic plugin.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-4257?
CVE-2026-4257 is a critical code injection vulnerability in supsysticcom Contact Form by Supsystic, published on 30 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-94
Which versions are affected by CVE-2026-4257?
How do I fix CVE-2026-4257?
No fix has been published for CVE-2026-4257 yet. Limit exposure of the affected software until one is available.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-4257 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-4257 exists.
Public exploit code: 1 Metasploit module, 1 Exploit-DB entry, 1 Nuclei template and 3 proofs of concept on GitHub.
Sources
Also known as GHSA-fgcr-fh9h-2fw9.