Summaryinfo

A vulnerability has been found in supsysticcom Contact Form by Supsystic Plugin up to 1.7.36 on WordPress and classified as critical. This issue affects the function registerUndefinedFilterCallback. This manipulation causes code injection. The identification of this vulnerability is CVE-2026-4257. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability classified as critical was found in supsysticcom Contact Form by Supsystic Plugin up to 1.7.36 on WordPress. Affected by this vulnerability is the function registerUndefinedFilterCallback. The manipulation with an unknown input leads to a code injection vulnerability. The CWE definition for the vulnerability is CWE-94. The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

The weakness was shared by Azril Fathoni. It is possible to read the advisory at wordfence.com. This vulnerability is known as CVE-2026-4257 since 03/16/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 03/31/2026). The attack technique deployed by this issue is T1059 according to MITRE ATT&CK.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-17239). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• WordPress Plugin

Vendor

• supsysticcom

Name

• Contact Form by Supsystic Plugin

Version

• 1.7.0
• 1.7.1
• 1.7.2
• 1.7.3
• 1.7.4
• 1.7.5
• 1.7.6
• 1.7.7
• 1.7.8
• 1.7.9
• 1.7.10
• 1.7.11
• 1.7.12
• 1.7.13
• 1.7.14
• 1.7.15
• 1.7.16
• 1.7.17
• 1.7.18
• 1.7.19
• 1.7.20
• 1.7.21
• 1.7.22
• 1.7.23
• 1.7.24
• 1.7.25
• 1.7.26
• 1.7.27
• 1.7.28
• 1.7.29
• 1.7.30
• 1.7.31
• 1.7.32
• 1.7.33
• 1.7.34
• 1.7.35
• 1.7.36

CPE 2.3info

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CPE 2.2info

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