CVE-2026-100671 Grav before 2.0.25 Session Cookie Theft via Twig Sandbox
Attackers with page-write permissions can steal administrator session cookies via Twig sandbox flaws, enabling account takeover.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-100671?
CVE-2026-100671 is a high-severity vulnerability in getgrav grav, published on 26 Sep 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
Grav is a flat-file CMS. In versions 2.0.19 through 2.0.24 — and in 2.0.0 through 2.0.18 and 1.7.x only where content Twig has been explicitly enabled — page content authored by a user holding only page-write permission is rendered through a Twig sandbox that allowlists get_cookie(), which returns any cookie sent with the current request, including the visitor's session cookie. Because the read occurs server-side via filter_input(INPUT_COOKIE, ...), the HttpOnly, Secure and SameSite attributes offer no protection. Grav then stores the finished post-Twig output in a page-content cache keyed only on page identity and the configuration checksum, with no session, user or request dimension and no bypass for authenticated visitors. A page published by a page-write user can therefore capture the session identifier of the next administrator who views it, after which the cached output serves that identifier to unauthenticated visitors, who can replay the cookie to authenticate as that administrator. Since 2.0.19, security.twig_content.process_enabled defaults to true and Security::applyTwigContentDefault() derives each page's process.twig flag from that gate, so content Twig runs on every page with no frontmatter or operator action. Fixed in 2.0.25; 1.7.x is outside the backport scope.
Weakness: CWE-200
Which versions are affected by CVE-2026-100671?
How do I fix CVE-2026-100671?
No fix has been published for CVE-2026-100671 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-100671 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100671 exists.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as GHSA-jcv9-gfgx-wjw4, GHSA-pp89-h475-7gj6.