# Grav CMS origin validation bypass in referrer header

Source: https://junglewise.ai/threats/grav-cms-origin-validation-bypass-in-referrer-header-0f775642  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-25. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

Severity: medium · CVSS 5.4 · Published 2026-08-25

Grav CMS is a flat-file content management system. Before version 2.0.16, it incorrectly validates the HTTP Referer header when checking if a request originates from the same website, using a flawed string comparison that accepts any domain starting with the site's name. An attacker controlling a lookalike domain (e.g., example.com.attacker.tld if the target is example.com) can bypass security checks designed to prevent cross-site attacks, potentially leading to unauthorized actions being treated as trusted.

Technologies: [getgrav/grav (Packagist)](https://junglewise.ai/threats/technologies/getgrav-grav). Vendors: [Packagist](https://junglewise.ai/threats/vendors/packagist).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Medium severity, with a CVSS score of 5.4, published 25 August 2026.

**Which products and versions are affected?** getgrav/grav (Packagist) < 2.0.16.

**Is there a fix for This vulnerability?** A patch was published on 2026-08-10: Patch released in version 2.0.16 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is This vulnerability attacked?** It is attacked over the network.

**Am I affected?** Check whether you run getgrav/grav (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a string prefix matching error (CWE-346: Origin Validation Error) in the Uri::referrer() and Pages::referrerRoute() methods. Both methods use str_starts_with($referrer, $base) where $base is the site's root URL without a trailing slash (e.g., "https://example.com"). This unanchored comparison accepts any Referer header that begins with that string, including "https://example.com.attacker.tld", allowing an attacker controlling a domain with the victim site's name as a prefix to bypass origin validation. The attack requires user interaction (the victim must click a link or be redirected from the attacker's site). A patch is available in version 2.0.16, which adds proper boundary checking with a trailing slash delimiter.

## Affected products

- Grav CMS < 2.0.16

## Timeline

- 2026-08-25: disclosed
- 2026-08-10: patched: Patch released in version 2.0.16

## References

- [https://github.com/getgrav/grav/security/advisories/GHSA-9ccq-2jfg-qw33](https://github.com/getgrav/grav/security/advisories/GHSA-9ccq-2jfg-qw33)

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