---
title: "CVE-2026-52889: Formie Hidden field defaults vulnerable to Server-Side Template Injection"
url: https://erroneo.us/security/cve/CVE-2026-52889/
description: "CVE-2026-52889 (verbb/formie (Composer (PHP))): Formie is a Craft CMS plugin for creating forms. Prior to 3.1.27, Formie can pass request-derived Hidden…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-08-19
date_modified: 2026-08-19
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-52889"
kev: false
cvss: 9.8
epss: 0.01274
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-52889: Formie Hidden field defaults vulnerable to Server-Side Template Injection

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 1.3% , percentile 70: FIRST’s model estimates a 1.3% chance of exploitation activity in the next 30 days, higher than 70% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes verbb/formie (Composer (PHP)) < 3.1.27, fixed in 3.1.27 . Check your lockfile, including transitive dependencies.

## What it is

Formie is a Craft CMS plugin for creating forms. Prior to 3.1.27, Formie can pass request-derived Hidden field defaults such as HTTP User Agent, Referer URL, Current URL, Current URL without Query String, Query Parameter, and Cookie Value to Craft's Twig rendering layer during front-end form rendering. An unauthenticated attacker can place Twig syntax in one of these request-controlled inputs when a public form contains an affected Hidden field. Hidden::getFrontEndInputOptions() then assigns the value to defaultValue and calls renderString, causing server-side template evaluation rather than treating the request data as a plain string. Depending on the Craft site configuration and available Twig capabilities, exploitation can disclose sensitive information, modify application state, or achieve remote code execution. This issue is fixed in version 3.1.27.

## Affected packages

- Composer (PHP) `verbb/formie` < 3.1.27 → fixed: 3.1.27

## Affected products (CVE record)

- verbb formie: < 3.1.27

## Severity

- GitHub_M CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 1.27% probability of exploitation activity in the next 30 days; percentile 70.

## Sources

- [GitHub Advisory GHSA-565m-g33j-jq96](https://github.com/advisories/GHSA-565m-g33j-jq96)
- [CVE.org record CVE-2026-52889](https://www.cve.org/CVERecord?id=CVE-2026-52889)
- [NVD entry CVE-2026-52889](https://nvd.nist.gov/vuln/detail/CVE-2026-52889)
- [github.com](https://github.com/verbb/formie/security/advisories/GHSA-565m-g33j-jq96)
- [github.com](https://github.com/verbb/formie/commit/d3b9d15290405e484e3b5c91c5d8fab93047f9b2)
- [github.com](https://github.com/verbb/formie/releases/tag/3.1.27)

---
Source page: https://erroneo.us/security/cve/CVE-2026-52889/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt