Public proof of concept

CVE-2026-4257

A public proof of concept exists; no exploitation attested.

Published2026-03-30
WeaknessCWE-94

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC

2026-03-3022:16CVE publishedNVD
2026-10-2319:23First public proof of conceptPoC-in-GitHub
2026-10-2319:23EPSS crossed 10 %FIRST EPSS

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-4257?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-4257?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

Neither OSV.dev nor the vendor advisories we read list affected versions for CVE-2026-4257 yet.

Full record on NVD

Fix

No fix published by the sources we read yet. NVD record

Detection

read 2026-10-23 19:25 UTC

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: 3 repositories, unverifiedbootstrapbool/cve-2026-4257shootcannon/CVE-2026-4257dann3xplo1t/CVE-2026-4257

Sources

NVDCVE recordread 2026-10-23
CISA-ADPSSVC decisionnone2026-03-31
OpenCVESSVC decisionnone—
CNACVSS 3.19.8read 2026-10-23
CNAweakness (CWE)CWE-94read 2026-10-23
FIRST EPSSEPSS score32.8 %read 2026-10-23
PoC-in-GitHubproof of concept3read 2026-10-23

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published: 2026-03-30
Last Modified: 2026-06-17
NVD status: Deferred

Frequently asked questions

What is CVE-2026-4257?

Is CVE-2026-4257 actively exploited?

Active exploitation of CVE-2026-4257 has not been confirmed. Its EPSS score was 32.8% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-4257?

CVE-2026-4257 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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