CVE-2026-4257

CRITICAL 9.8

Contact Form by Supsystic <= 1.7.36 - Unauthenticated Server-Side Template Injection via Prefill Functionality

CVSS Score

9.8

EPSS Score

19.6%

EPSS Percentile

95th

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.

CWE	CWE-94
Vendor	supsysticcom
Product	contact form by supsystic
Published	Mar 30, 2026
Last Updated	Apr 8, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector

Attack Complexity

Privileges Required

User Interaction

Scope

Confidentiality

Integrity

Availability

Affected Versions

supsysticcom / Contact Form by Supsystic

0 ≤ 1.7.36

References

NVD ↗ CVE.org ↗ EPSS Data ↗

wordfence.com: https://www.wordfence.com/threat-intel/vulnerabilities/id/415c9658-bfb2-453b-a697-c63c08b0ca61?source=cve plugins.trac.wordpress.org: https://plugins.trac.wordpress.org/browser/contact-form-by-supsystic/tags/1.7.36/modules/forms/views/forms.php#L323 plugins.trac.wordpress.org: https://plugins.trac.wordpress.org/changeset/3491826/contact-form-by-supsystic

Credits

Azril Fathoni