CVE-2017-9442 in BigTree
Summary
by MITRE
** DISPUTED ** BigTree CMS through 4.2.18 allows remote authenticated users to execute arbitrary code by uploading a crafted package containing a PHP web shell, related to extraction of a ZIP archive to filename patterns such as cache/package/xxx/yyy.php. This issue exists in core\admin\modules\developer\extensions\install\unpack.php and core\admin\modules\developer\packages\install\unpack.php. NOTE: the vendor states "You must implicitly trust any package or extension you install as they all have the ability to write PHP files."
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 08/05/2024
The vulnerability CVE-2017-9442 represents a critical remote code execution flaw in BigTree CMS versions through 4.2.18 that demonstrates a fundamental security oversight in package installation and file extraction processes. This issue arises from improper handling of ZIP archive extraction operations where the application fails to adequately validate or sanitize file paths during the unpacking process. The vulnerability specifically affects the core admin modules responsible for package and extension installation, namely the developer extensions install functionality and packages install functionality located at core/admin/modules/developer/extensions/install/unpack.php and core/admin/modules/developer/packages/install/unpack.php respectively. The flaw enables authenticated attackers to upload malicious packages containing PHP web shells that can be executed within the context of the web server, creating a persistent backdoor access vector.
The technical exploitation of this vulnerability relies on the improper validation of filename patterns during ZIP extraction operations. When a malicious package is uploaded and processed, the system extracts files to predetermined cache directories using patterns such as cache/package/xxx/yyy.php, allowing attackers to place executable PHP code in locations where it can be accessed through web requests. This represents a classic path traversal and file injection vulnerability where the application does not properly validate that extracted filenames do not contain malicious path components or executable code. The vulnerability maps to CWE-22 Path Traversal and CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component, both of which are commonly exploited in web application attacks. From an operational perspective, this vulnerability enables attackers to establish persistent access to the affected system, potentially leading to full compromise of the web server and underlying infrastructure.
The impact of this vulnerability extends beyond simple code execution as it fundamentally undermines the trust model of the CMS package management system. The vendor's statement regarding implicit trust in installed packages highlights a dangerous security assumption that places the burden of security validation entirely on the user rather than implementing proper sandboxing or validation mechanisms within the application itself. This vulnerability aligns with ATT&CK technique T1059.007 Command and Scripting Interpreter: PHP, which describes the use of PHP scripts to execute commands on compromised systems. The attack surface is particularly concerning because it leverages legitimate administrative functionality to achieve malicious code execution, making detection more difficult as the activity appears to be normal administrative behavior. The issue demonstrates a critical failure in input validation and privilege separation, where authenticated users with package installation privileges can escalate their access to full system compromise.
Organizations should implement immediate mitigations including restricting package installation privileges to only trusted administrators, implementing strict file type validation for uploaded packages, and monitoring for suspicious file creation patterns in cache directories. Network-based solutions should monitor for unusual file extraction patterns and PHP file creation in web-accessible directories. The vulnerability highlights the importance of principle of least privilege and proper input validation in web applications. Security teams should also consider implementing application whitelisting policies that prevent arbitrary PHP code execution in sensitive directories, and regular security audits should verify that no malicious files exist in package cache directories. The incident underscores the critical need for proper sandboxing of package installation processes and demonstrates how seemingly legitimate administrative functionality can be weaponized when proper security controls are absent from the application architecture.