Contact Form by Supsystic <= 1.7.36 - Unauthenticated Server-Side Template Injection via Prefill Functionality
Strategic Overview
- Status
- Patched in 1.8.0
- Affected Plugin
- Contact Form by Supsystic
- Affected Version
<= 1.7.36- CVSS
- 9.8Critical
- Weakness type
- CWE-94 · Improper Control of Generation of Code ('Code Injection')
- CVE
CVE-2026-4257
At a glance
CVE-2026-4257 is a critical-severity Improper Control of Generation of Code ('Code Injection') vulnerability in the Contact Form by Supsystic WordPress plugin, affecting versions <= 1.7.36. It carries a CVSS score of 9.8 (reachable over the network; low attack complexity; high confidentiality, integrity, availability impact). Exploitation requires no authentication. The issue is fixed in version 1.8.0; sites on affected versions should update now. Disclosed March 2026, reported by Azril Fathoni (kiseki).
Vulnerability Overview
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.
Technical Analysis
The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no privileges on the target site, and no interaction from a victim user. A successful exploit has high impact on confidentiality, integrity, availability — full site compromise territory.
CWE-94: Improper Control of Generation of Code ('Code Injection')
Contact Form by Supsystic <= 1.7.36 carries this weakness at registerUndefinedFilterCallback(), and reaching it takes no account at all. Code injection means input from a request reaches a language construct that evaluates code, so the attacker's text is executed rather than treated as data.
The injected code runs with the web server's privileges, giving the attacker the same access to the database and filesystem as WordPress itself. For Contact Form by Supsystic the fix is 1.8.0: builds <= 1.7.36 are affected, anything from 1.8.0 onward is not.
Remediation
Update to version 1.8.0, or a newer patched version
How does WordSec protect against this?
Requests carrying this pattern arrive without a session, so nothing upstream of the firewall gets a chance to reject them: WordSec's web application firewall inspects request payloads before WordPress loads them. Classes like this one can leave something behind, so the staged malware scanner is the second half: it looks for dropped files and modified code rather than for the request that created them. None of that substitutes for the fix: Contact Form by Supsystic 1.8.0 closes this, and updating the plugin is the step that ends it.
- Firewall
- Scanner
- Login Security
External References
Related records
Same weakness class
Other vulnerabilities in Contact Form by Supsystic
- 8.8Contact Form by Supsystic <= 1.7.10 SQL Injections
- 7.2CVE-2026-83625: Contact Form by Supsystic <= 1.10.2 Stored XSS
CVE-2026-83625 - 7.2CVE-2026-73378: Contact Form by Supsystic < 1.10.0 Stored XSS
CVE-2026-73378 - 6.1CVE-2025-52753: Contact Form by Supsystic <= 1.7.36 Reflected XSS
CVE-2025-52753 - 6.1CVE-2024-13452: Contact Form by Supsystic CSRF
CVE-2024-13452 - 6.1CVE-2021-24276: Contact Form by Supsystic <= 1.7.14 Reflected XSS
CVE-2021-24276 - 5.5Contact Form by Supsystic < 1.7.20 Stored Cross-Site Scripting
- 5.4CVE-2023-2528: Contact Form by Supsystic <= 1.7.24 CSRF
CVE-2023-2528
Vulnerability data © Defiant, Inc., provided under the Wordfence Intelligence T&C