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Grav's Twig processing allowing dangerous PHP functions by default

High severity GitHub Reviewed Published Apr 13, 2021 in getgrav/grav • Updated Jan 29, 2023

Package

composer getgrav/grav (Composer)

Affected versions

<= 1.7.10

Patched versions

1.7.11

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

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.

References

@rhukster rhukster published to getgrav/grav Apr 13, 2021
Reviewed Apr 13, 2021
Published by the National Vulnerability Database Apr 13, 2021
Published to the GitHub Advisory Database Apr 16, 2021
Last updated Jan 29, 2023

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
High
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H

EPSS score

5.097%
(93rd percentile)

Weaknesses

CVE ID

CVE-2021-29440

GHSA ID

GHSA-g8r4-p96j-xfxc

Source code

No known source code
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