What is CVE-2026-4257?

CVE-2026-4257 is a critical-severity vulnerability in Supsysticcom Contact Form By Supsystic, classified under Code Injection. CVSS score: 9.8/10. Published 2026-03-30.

How severe is CVE-2026-4257?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2026-4257 known to be exploited?

4 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

RCE in Supsysticcom Contact Form By Supsystic

CVE-2026-4257

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.

Vulnerability class: RCE (Remote Code Execution)

EPSS: 0.415 (98.6th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Affected products

Supsysticcom Contact Form By Supsystic — versions 0

Weakness classification (CWE)

CWE-94 — Code Injection

Public proof-of-concept exploits

References

Frequently asked questions

What is CVE-2026-4257?: CVE-2026-4257 is a critical-severity vulnerability in Supsysticcom Contact Form By Supsystic, classified under Code Injection. CVSS score: 9.8/10. Published 2026-03-30.
How severe is CVE-2026-4257?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2026-4257 known to be exploited?: 4 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.