CVE-2023-34252: Grav Server-side Template Injection via Insufficient Validation in filterFilter
Grav is a file-based Web platform. Prior to version 1.7.42, there is a logic flaw in the GravExtension.filterFilter() function whereby validation against a denylist of unsafe functions is only performed when the argument passed to filter is a string. However, passing an array as a callable argument allows the validation check to be skipped. Consequently, a low privileged attacker with login access to Grav Admin panel and page creation/update permissions is able to inject malicious templates to obtain remote code execution. The vulnerability can be found in the GravExtension.filterFilter() function declared in /system/src/Grav/Common/Twig/Extension/GravExtension.php. Version 1.7.42 contains a patch for this issue. End users should also ensure that twig.undefinedfunctions and twig.undefinedfilters properties in /path/to/webroot/system/config/system.yaml configuration file are set to false to disallow Twig from treating undefined filters/functions as PHP functions and executing them.
Other sources
Grav is a flat-file content management system. Prior to version 1.7.42, there is a logic flaw in the GravExtension.filterFilter() function whereby validation against a denylist of unsafe functions is only performed when the argument passed to filter is a string. However, passing an array as a callable argument allows the validation check to be skipped. Consequently, a low privileged attacker with login access to Grav Admin panel and page creation/update permissions is able to inject malicious templates to obtain remote code execution. The vulnerability can be found in the GravExtension.filterFilter() function declared in /system/src/Grav/Common/Twig/Extension/GravExtension.php. Version 1.7.42 contains a patch for this issue. End users should also ensure that twig.undefinedfunctions and twig.undefinedfilters properties in /path/to/webroot/system/config/system.yaml configuration file are set to false to disallow Twig from treating undefined filters/functions as PHP functions and executing them.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
grav/GravExtension.filterFilter()to a version that resolves this vulnerability.Fixed in 1.7.42 - Configuration
Set `twig.undefined_functions` to `false` in `/path/to/webroot/system/config/system.yaml` to disallow Twig from treating undefined functions as PHP functions and executing them.
Grav twig.undefined_functions = false - Configuration
Set `twig.undefined_filters` to `false` in `/path/to/webroot/system/config/system.yaml` to disallow Twig from treating undefined filters as PHP functions and executing them.
Grav twig.undefined_filters = false
Event History
Frequently Asked Questions
What is CVE-2023-34252?
CVE-2023-34252 is a logic flaw vulnerability in the Grav file-based Web platform, specifically in the `GravExtension.filterFilter()` function.
What is the severity of CVE-2023-34252?
The severity of CVE-2023-34252 is high, with a severity value of 7.2.
How does CVE-2023-34252 affect the software?
CVE-2023-34252 affects the Grav Web platform prior to version 1.7.42.
How does CVE-2023-34252 work?
CVE-2023-34252 is a logic flaw whereby validation against a denylist of unsafe functions is only performed when the argument passed to filter is a string, allowing an array to be passed as a callable argument.
How can CVE-2023-34252 be fixed?
To fix CVE-2023-34252, users are advised to update to version 1.7.42 or later of the Grav Web platform.