CVE-2026-52889 is a critical-severity (CVSS 9.8) CWE-1336 vulnerability in verbb/formie. A fix is available for verbb/formie — see the affected versions and patch details below.
Formie: Server-Side Template Injection in Formie Hidden field defaults
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-52889 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
verbb/formieReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Formie Hidden fields could evaluate request-derived values as Twig during front-end form rendering.
When a Hidden field used a dynamic default value such as HTTP User Agent, Referer URL, Current URL, Query Parameter, or Cookie Value, the value was copied from the incoming request and later passed to Craft’s Twig rendering layer. This allowed an unauthenticated attacker to provide Twig syntax in request-controlled input and have it evaluated server-side when the form was rendered.
Affected Versions
verbb/formie for Craft 5:
- Affected: >= 3.0.0-beta.1, <= 3.1.26
- Patched: 3.1.27
Impact
An unauthenticated attacker could trigger server-side template evaluation by visiting a public form containing a Hidden field configured with a request-derived default value.
Because Craft’s normal Twig environment exposes application objects, this may lead to disclosure of sensitive information, modification of application state, or remote code execution depending on the site configuration and available Twig capabilities.
Technical Details
The issue exists in the Hidden field front-end render path. Request-derived Hidden field defaults were assigned to the field’s defaultValue, then rendered via Twig in Hidden::getFrontEndInputOptions().
The fix ensures Twig rendering is only performed for the custom default option, where the template source is admin-authored. Request-derived default options are now treated as plain strings.
Patches
Update to Formie 3.1.27 or later.
Workarounds
Until patched, avoid using request-derived Hidden field defaults on public forms, including:
- HTTP User Agent
- HTTP Refer URL
- Current URL
- Current URL without Query String
- Query Parameter
- Cookie Value
Alternatively, remove affected Hidden fields from public forms until the update is applied.
Credit
Name: Yanchon918s Email: [email protected]
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | verbb/formie | all versions | 3.1.27composer require verbb/formie:^3.1.27 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for verbb/formie, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update verbb/formie to 3.1.27 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-52889 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-52889 in your dependencies?
Find it across Packagist, including transitive dependencies.