CVE-2021-29440

HIGH8.4EPSS 11.2%

Grav's Twig processing allowing dangerous PHP functions by default

Published: 4/16/2021Modified: 5/4/2026

Description

### Impact Twig processing of static pages can be enabled in the front matter by any administrative user allowed to create or edit pages. As the Twig processor runs unsandboxed, this behavior can be used to gain arbitrary code execution and elevate privileges on the instance. ### Patches The issue was addressed by preventing dangerous functions from being called in Twig templates. A configuration option has been added to manually allow arbitrary PHP functions (`system.twig.safe_functions`) and filters (`system.twig.safe_filters`). Futures major versions of Grav may disable this functionality by default. ### Workarounds Blocking access to the `/admin` path from untrusted sources will reduce the probability of exploitation. ### References - https://portswigger.net/research/server-side-template-injection - https://blog.sonarsource.com/grav-cms-code-execution-vulnerabilities ### For more information If you have any questions or comments about this advisory, you can contact: - The original reporters, by sending an email to vulnerability.research [at] sonarsource.com; - The maintainers, by opening an issue on this repository.

Affected packages (1)

CVSS scores

SourceVersionSeverityVector
osvCVSS 3.1HIGH8.4CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H

References (5)