CVE-2019-19576 in class.upload
Summary
by MITRE
class.upload.php in verot.net class.upload before 1.0.3 and 2.x before 2.0.4, as used in the K2 extension for Joomla! and other products, omits .phar from the set of dangerous file extensions.
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Analysis
by VulDB Data Team • 06/26/2026
The vulnerability identified as CVE-2019-19576 resides within the class.upload.php library developed by verot.net, which serves as a file upload handling component in various web applications including the popular K2 extension for Joomla!. This flaw affects versions prior to 1.0.3 and 2.x versions prior to 2.0.4, creating a significant security gap that could be exploited by malicious actors. The vulnerability specifically concerns the library's file extension validation mechanism, where it fails to properly block .phar files from being uploaded to the target system. This omission represents a critical oversight in the security controls designed to prevent the execution of potentially malicious files through file upload interfaces.
The technical flaw stems from an incomplete blacklist implementation within the class.upload.php library where the developers failed to include the .phar file extension in their list of forbidden extensions. This oversight allows attackers to upload files with .phar extensions that can be executed in certain server configurations, particularly when PHP is configured to process .phar files as executable code. The .phar extension is particularly dangerous because it represents PHP Archive files which can contain serialized PHP objects and executable code, making them a preferred vector for remote code execution attacks. This vulnerability is categorized under CWE-434, which addresses the improper restriction of file uploads, and represents a classic example of inadequate input validation and sanitization.
The operational impact of this vulnerability is substantial, particularly within the Joomla! ecosystem where the K2 extension is widely deployed. When exploited, this flaw allows attackers to upload malicious .phar files that could potentially execute arbitrary code on the target server, leading to complete system compromise. The attack vector typically involves uploading a .phar file through a vulnerable file upload interface, followed by triggering its execution through a subsequent request to the server. This could result in unauthorized access, data theft, system infiltration, and potential lateral movement within the network. The vulnerability is particularly concerning because it affects widely used web applications and content management systems, making it a prime target for automated exploitation tools.
The mitigation strategy for CVE-2019-19576 requires immediate patching of the affected class.upload.php library to include .phar in the list of blocked file extensions. Organizations should also implement additional security controls including server-side file type validation, content-type checking, and proper file name sanitization. Network-based detection measures should be deployed to monitor for suspicious file upload activities and .phar file patterns in traffic. Security teams should also review their existing file upload validation mechanisms and ensure that all potentially dangerous file extensions are properly blocked, including .phtml, .php3, .php4, .php5, and others as defined in the ATT&CK framework's T1190 technique for exploiting file upload vulnerabilities. Regular security audits and dependency management practices should be implemented to prevent similar oversights in other third-party libraries and components.