CVE-2021-29440

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.

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.

Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.

CVE-2021-29440 has a CVSS score of 8.4 (High). The vector is network-reachable, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.7.11); upgrading removes the vulnerable code path.

Kodem intelligence

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.

1. What is CVE-2021-29440? CVE-2021-29440 is a high-severity code injection vulnerability in getgrav/grav (composer), affecting versions <= 1.7.10. It is fixed in 1.7.11. Untrusted input is evaluated as executable code within the application's runtime environment.
2. How severe is CVE-2021-29440? CVE-2021-29440 has a CVSS score of 8.4 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of getgrav/grav are affected by CVE-2021-29440? getgrav/grav (composer) versions <= 1.7.10 is affected.
4. Is there a fix for CVE-2021-29440? Yes. CVE-2021-29440 is fixed in 1.7.11. Upgrade to this version or later.
5. Is CVE-2021-29440 exploitable, and should I be worried? Whether CVE-2021-29440 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-29440 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-29440? Upgrade getgrav/grav to 1.7.11 or later.

Other vulnerabilities in getgrav/grav