Grav Form Plugin has an Anonymous Page Content Overwrite via Form File Upload filename Override

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

7.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P · score source

EPSS

• CVE-2026-42845: 0.74% estimated exploitation activity in the next 30 days; percentile 54.68 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary (Tested on Form 9.0.3 released on April, 28th) The Form plugin's file upload handler at user/plugins/form/classes/Form.php:583 accepts a POST-supplied filename parameter ($filename = $post['filename'] ?? $upload['file']['name']) that overrides the original uploaded filename. The override passes through Utils::checkFilename(), which blocks only a narrow extension list (.php, .htm, .js, .exe). Markdown (.md) is not blocked. A page's directory under user/pages/ contains its .md content file (e.g. default.md, form.md). When a form's file upload field has accept: [''] (or any policy that admits text files), an unauthenticated visitor can: 1. Upload arbitrary content with filename=form.md (or other page-content filenames), 2. Submit the form to trigger Form::copyFiles(), which overwrites the page's own .md file. Details Vulnerable code path user/plugins/form/classes/Form.php:580-606 (in uploadFiles()): Utils::checkFilename() (system/src/Grav/Common/Utils.php:980) blocks ..,…

Published by the source

6 May 2026, 23:03 UTC

Last modified by the source

13 May 2026, 14:04 UTC

Source last checked

26 Oct 2026, 14:40 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-w4rc-p66m-x6qq

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-42845

Advisory: Grav Form Plugin has an Anonymous Page Content Overwrite via Form File Upload filename Override
IDs: CVE-2026-42845, GHSA-w4rc-p66m-x6qq
Record: https://patchnext.com/advisories/cve-2026-42845 (revision 1, source checked 26 Oct 2026, 14:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: getgrav/grav-plugin-form 9.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist getgrav/grav-plugin-form: affected < 9.1.0; fixed in 9.1.0

## Suggested inspection (read-only)
- Packagist getgrav/grav-plugin-form: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on getgrav/grav-plugin-form.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-w4rc-p66m-x6qq (GitHub-reviewed advisory GHSA-w4rc-p66m-x6qq lists affected ranges: Packagist getgrav/grav-plugin-form >=0 <9.1.0)

Commands are suggestions: review each one before running it.