K2 Arbitrary PHP Code Execution via Malicious File Upload

Executive Summary

This vulnerability exists in the K2 frontend article-attachment upload path, which allows files with a .php extension to be uploaded.

Because Apache's mod_php module executes files ending with .php, an attacker with K2 Author privileges can upload a file named shell.php.

Once uploaded, the attacker can access and execute this shell.php file on the web server, running arbitrary PHP code with the web server's permissions.

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Impact Analysis

An attacker exploiting this vulnerability can execute arbitrary PHP code on the web server.

This can lead to unauthorized access, data theft, server compromise, or further attacks within the affected environment.

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Compliance Impact

This vulnerability allows a K2 Author to upload and execute arbitrary PHP code on the web server, potentially leading to unauthorized access, data breaches, or manipulation of sensitive information.

Such unauthorized code execution and potential data compromise can negatively impact compliance with common standards and regulations like GDPR and HIPAA, which require protection of personal and sensitive data against unauthorized access and breaches.

Therefore, exploitation of this vulnerability could result in violations of these regulations due to insufficient security controls and exposure of protected data.

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Detection Guidance

This vulnerability involves the upload of `.php` files through the K2 frontend article-attachment upload path, which are then executed by Apache's mod_php. To detect this vulnerability on your system, you can check for the presence of suspicious `.php` files in the `/media/k2/attachments/` directory.

• Use commands to list `.php` files in the attachments directory, for example: `find /path/to/joomla/media/k2/attachments/ -name '*.php'`.
• Check web server access logs for requests to `.php` files under `/media/k2/attachments/`, e.g., `grep '/media/k2/attachments/.*\.php' /var/log/apache2/access.log`.
• Monitor for unusual or unauthorized file uploads by K2 Authors, especially files named like `shell.php`.

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Mitigation Strategies

Immediate mitigation steps include preventing the upload and execution of `.php` files through the K2 article-attachment upload path.

• Restrict file uploads in K2 to disallow `.php` extensions or any executable scripts.
• Configure the web server to deny execution of PHP files in the `/media/k2/attachments/` directory, for example by disabling PHP execution in that directory via Apache configuration.
• Review and limit the permissions of K2 Authors to prevent unauthorized file uploads.
• Remove any existing suspicious `.php` files from the attachments directory.

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