Grav CMS origin validation bypass in referrer header

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). 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

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