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.undefined_functions
and twig.undefined_filters
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.
The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.
Name | Vendor | Start Version | End Version |
---|---|---|---|
Grav | Getgrav | * | 1.7.42 (excluding) |
When a product allows a user’s input to contain code syntax, it might be possible for an attacker to craft the code in such a way that it will alter the intended control flow of the product. Such an alteration could lead to arbitrary code execution. Injection problems encompass a wide variety of issues – all mitigated in very different ways. For this reason, the most effective way to discuss these weaknesses is to note the distinct features which classify them as injection weaknesses. The most important issue to note is that all injection problems share one thing in common – i.e., they allow for the injection of control plane data into the user-controlled data plane. This means that the execution of the process may be altered by sending code in through legitimate data channels, using no other mechanism. While buffer overflows, and many other flaws, involve the use of some further issue to gain execution, injection problems need only for the data to be parsed. The most classic instantiations of this category of weakness are SQL injection and format string vulnerabilities.