CVE-2025-66299: Security Sandbox Bypass with SSTI (Server Side Template Injection) in the Grav CMS

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2025-12-01 · updated 2026-09-26
Weakness: CWE-94

Description

Grav is a file-based Web platform. Prior to 1.8.0-beta.27, Grav CMS is vulnerable to a Server-Side Template Injection (SSTI) that allows any authenticated user with editor permissions to execute arbitrary code on the remote server, bypassing the existing security sandbox. Since the security sandbox does not fully protect the Twig object, it is possible to interact with it (e.g., call methods, read/write attributes) through maliciously crafted Twig template directives injected into a web page. This allows an authenticated editor to add arbitrary functions to the Twig attribute system.twig.safe_filters, effectively bypassing the Grav CMS sandbox. This vulnerability is fixed in 1.8.0-beta.27.

Affected products

getgrav grav: before 1.8.0; 1.8.0-beta1, 1.8.0-beta10, 1.8.0-beta11, 1.8.0-beta12, 1.8.0-beta13, 1.8.0-beta14 (+20) — fixed in 1.8.0

How to fix

Upgrade to a fixed version: getgrav grav 1.8.0. Check the vendor advisory for mitigations.

References

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