Grav has Unauthenticated Path Traversal & Arbitrary File Write in its FormFlash component

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-42608: 0.60% estimated exploitation activity in the next 30 days; percentile 48.90 (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.

Vulnerability Report: Grav CMS Unauthenticated Path Traversal & Arbitrary File Write [ZERO-DAY] Unauthenticated Path Traversal leading to Arbitrary Directory Creation and Configuration Injection Summary Grav CMS (v1.7.49.5 and latest development source) is vulnerable to a Zero-Day Path Traversal vulnerability within the FormFlash core component. By manipulating the sessionid (passed as form-flash-id in POST requests), an unauthenticated attacker can traverse the filesystem to create arbitrary directories and write an index.yaml file containing attacker-controlled data. This vulnerability can lead to unauthorized modification of application behavior, potential data integrity issues, and service disruption in production environments. Affected Component - Versions: Confirmed in Grav v1.7.49.5 (latest stable) and the latest development source (March 2026). - Class: Grav\Framework\Form\FormFlash - Method: construct() / getTmpDir() - Parameter: sessionid (Mapped to form-flash-id in POST…

Published by the source

5 May 2026, 21:34 UTC

Last modified by the source

13 May 2026, 13:52 UTC

Source last checked

26 Oct 2026, 14:40 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-hmcx-ch82-3fv2

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# Patch Next advisory brief: CVE-2026-42608

Advisory: Grav has Unauthenticated Path Traversal & Arbitrary File Write in its FormFlash component
IDs: CVE-2026-42608, GHSA-hmcx-ch82-3fv2
Record: https://patchnext.com/advisories/cve-2026-42608 (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 8.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: getgrav/grav 2.0.0-beta.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist getgrav/grav: affected < 2.0.0-beta.2; fixed in 2.0.0-beta.2

## Suggested inspection (read-only)
- Packagist getgrav/grav: 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.
- 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-hmcx-ch82-3fv2 (GitHub-reviewed advisory GHSA-hmcx-ch82-3fv2 lists affected ranges: Packagist getgrav/grav >=0 <2.0.0-beta.2)

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