CVE-2015-6833 in PHP
Summary
by MITRE
Directory traversal vulnerability in the PharData class in PHP before 5.4.44, 5.5.x before 5.5.28, and 5.6.x before 5.6.12 allows remote attackers to write to arbitrary files via a .. (dot dot) in a ZIP archive entry that is mishandled during an extractTo call.
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Analysis
by VulDB Data Team • 07/03/2022
The CVE-2015-6833 vulnerability represents a critical directory traversal flaw within PHP's PharData class implementation, affecting multiple PHP version branches including 5.4.x through 5.4.43, 5.5.x through 5.5.27, and 5.6.x through 5.6.11. This vulnerability stems from improper handling of directory traversal sequences within ZIP archive entries during extraction operations, creating a significant security risk for applications that process untrusted archive files. The flaw specifically manifests when the extractTo method processes ZIP archive entries containing .. (dot dot) sequences that should normally be sanitized or rejected during archive extraction. This vulnerability directly maps to CWE-22, which defines improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. The issue enables attackers to bypass normal file system access controls and write files to arbitrary locations on the target system, potentially leading to arbitrary code execution or system compromise.
The technical exploitation of this vulnerability occurs when PHP applications utilize the PharData class to process untrusted ZIP archives, particularly in web applications that accept file uploads or download archives from external sources. During the extractTo operation, the system fails to properly sanitize or validate directory traversal sequences within archive entries, allowing attackers to manipulate the extraction path. When a ZIP archive contains entries with .. sequences in their paths, the extraction logic does not adequately restrict these paths, enabling the creation of files outside the intended extraction directory. This behavior creates a pathway for attackers to write malicious files to sensitive system locations such as web root directories, configuration files, or system binaries. The vulnerability is particularly dangerous in web environments where user-supplied ZIP archives are processed without proper validation, as it can enable remote code execution through the creation of web shells or modification of critical system files.
The operational impact of CVE-2015-6833 extends beyond simple file system manipulation to encompass potential system compromise and data exfiltration capabilities. Attackers can leverage this vulnerability to escalate privileges, install persistent backdoors, or modify application configuration files to redirect traffic or disable security controls. The vulnerability is particularly concerning in environments where PHP applications process files from untrusted sources, such as file upload functionalities, content management systems, or web-based archive processing services. This flaw can be exploited in conjunction with other vulnerabilities to create more sophisticated attack chains, potentially enabling attackers to achieve full system compromise. The vulnerability also aligns with ATT&CK technique T1059.007 for execution through web shells and T1078 for valid accounts and T1566 for spearphishing attachments, making it a valuable entry point for attackers seeking persistent access to compromised systems. Organizations running affected PHP versions face significant risk of unauthorized file system access and potential complete system compromise.
Mitigation strategies for CVE-2015-6833 primarily focus on immediate software updates and application-level defenses. The most effective solution involves upgrading to patched PHP versions, specifically PHP 5.4.44, 5.5.28, or 5.6.12, which contain the necessary fixes for proper directory traversal handling during ZIP archive extraction. Organizations should implement comprehensive patch management processes to ensure all affected systems receive updates promptly. Additionally, applications should validate and sanitize all archive entries before processing, particularly by implementing strict path validation that rejects entries containing .. sequences or absolute paths. Input validation should include checking for directory traversal patterns and ensuring that all extracted file paths remain within the intended extraction directory. Security controls should also include restricting the permissions of PHP processes and implementing proper file system access controls to limit the impact of successful exploitation attempts. Network-level protections such as web application firewalls can provide additional defense in depth, though they should not be relied upon as the sole mitigation. Regular security auditing of applications that process user-supplied archives is essential to identify and remediate similar vulnerabilities in custom code implementations.