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

> Unauthenticated attackers can execute arbitrary code via Server-Side Template Injection in the Contact Form by Supsystic plugin.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 30 Mar 2026
- **Updated:** 8 Apr 2026
- **Also known as:** GHSA-fgcr-fh9h-2fw9

## What is CVE-2026-4257?

CVE-2026-4257 is a critical code injection vulnerability in supsysticcom Contact Form by Supsystic, published on 30 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-4257?


## How do I fix CVE-2026-4257?

No fix has been published for CVE-2026-4257 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-4257 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-4257 exists.

Public exploit code:

- CVE-2026-4257 - Contact Form by Supsystic <= 1.7.36 # SSTI to RCE  (github_poc): https://github.com/dann3xplo1t/CVE-2026-4257
- Supsystic Contact Form Wordpress Plugin SSTI RCE (metasploit)
- https://github.com/bootstrapbool/cve-2026-4257 (github_poc): https://github.com/bootstrapbool/cve-2026-4257
- SSTI contact form to rce (github_poc): https://github.com/shootcannon/CVE-2026-4257
- WordPress Plugin Supsystic Contact Form 1.7.36 - SSTI (exploitdb)
- WordPress Contact Form by Supsystic - Server-Side Template Injection (nuclei): http/cves/2026/CVE-2026-4257.yaml

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-4257 and fix it if it is affected.

What it is: CVE-2026-4257 is a critical code injection vulnerability in supsysticcom Contact Form by Supsystic, published on 30 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-4257 exists.

Affected product: supsysticcom Contact Form by Supsystic. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-4257/ (Markdown: https://insights.sbomify.com/CVE-2026-4257/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-4257
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-4257
- OSV: https://osv.dev/vulnerability/CVE-2026-4257

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-4257/
Summaries are generated and may contain mistakes; the official description above is the record.