Deserialization of Untrusted Data Affecting typo3/phar-stream-wrapper package, versions >=2.0.0, <2.1.1 >=3.0.0, <3.1.1

typo3/phar-stream-wrapper is a stream handler package for a popular content management system.

Affected versions of this package are vulnerable to Deserialization of Untrusted Data. Insecure deserialization is a vulnerability which occurs when untrusted data is used to abuse the logic of an application.

Due to missing sanitisation of user input, Phar files can be invoked by manipulated URLs in TYPO3 backend forms. A valid backend user account is needed to exploit this vulnerability. This vulnerability can be triggered to bypass protection of the PharStreamWrapper interceptor through file invocations such as file_exists or stat in order to exploit path traversal attacks, which can lead to abusing application logic leading to deserialization attacks.

<?php
// Helper::determineBaseFile(
//    'phar:///path/bad.phar/../good.phar'
// )
// is incorrectly resolved to
// base name '/path/good.phar'
// ... which is used in order to allow invocation
if ($interceptor->assert('/path/good.phar')) {
    $wrapper->invokeInternalStreamWrapper(
      'stat',
      'phar:///path/bad.phar/../good.phar'
    );
}

Serialization is a process of converting an object into a sequence of bytes which can be persisted to a disk or database or can be sent through streams. The reverse process of creating object from sequence of bytes is called deserialization. Serialization is commonly used for communication (sharing objects between multiple hosts) and persistence (store the object state in a file or a database).

Deserialization of untrusted data (CWE-502), is when the application deserializes untrusted data without sufficiently verifying that the resulting data will be valid, letting the attacker to control the state or the flow of the execution.

An attacker just needs to identify a piece of software that has both a vulnerable class on its path, and performs deserialization on untrusted data. Then all they need to do is send the payload into the deserializer, getting the command executed.

• GitHub Commit

• TYPO3 Advisory