Grav CMS versions 2.0.0-rc.1 through 2.0.21 contain a vulnerability in the Twig content sandbox implementation. The sandbox fails to restrict the dump and serialize filters (print_r, vardump, json_encode, yaml_encode, string) because GravExtension::assertSandboxDumpSafe() calls SandboxExtension::isSandboxed() without a Source argument, which only checks a global sandbox flag that Grav never enables. Consequently, an authenticated user with page-edit permissions can render Twig content such as {{ config|print_r }} to dump the entire merged configuration, bypassing path redaction and exposing sensitive plugin secrets including SMTP credentials, API tokens, webhook secrets, and cache backend passwords. Grav 1.7 is not affected as it does not include a Twig content sandbox. The vulnerability is addressed in Grav 2.0.22 by registering the affected filters with Twig's needs_is_sandboxed flag.

An authenticated user with page-edit rights can access and disclose sensitive configuration data including credentials and secrets. This exposure can lead to further compromise of the system or connected services. The vulnerability does not require privilege escalation beyond page-edit rights but allows unauthorized disclosure of sensitive information.

Upgrade Grav CMS to version 2.0.22 or later, where the vulnerability is fixed by properly restricting the affected Twig filters. No other mitigations are indicated by the vendor advisory.