Researchers from Sucuri have identified a high-risk vulnerability in the WordPress Download Manager plugin that can be exploited to upload backdoors to affected websites.
WordPress Download Manager is a management plugin for files and documents that has been downloaded more than 850,000 times from the official WordPress website.
Sucuri discovered that the plugin is plagued by a remote code execution/remote file inclusion vulnerability that can be leveraged to hijack WordPress websites by injecting backdoors and modifying administrator credentials.
“The plugin used a custom method to handle certain types of Ajax requests which could be abused by an attacker to call arbitrary functions within the application’s context,” Sucuri’s Mickael Nadeau explained in a blog post. “There were no permission checks before handling these special Ajax calls. This allowed a malicious individual (with a minimal knowledge of WordPress internals) to inject a backdoor on the remote site or to change the administrator’s password if the name of his account was known.”
According to Nadeau, the “wpdm_ajax_call_exec()” function could be used to call any other function available within the current execution context. During their tests, researchers called the “wpdm_upload_icon()” function, which allowed them to upload arbitrary files to the “file-type-icons” directory. An attacker could use this method to upload a backdoor and take control of the targeted website.
Sucuri has pointed out that the attack only works if an attacker can generate a valid nonce, a WordPress-generated string that acts as a special token and which is utilized to identify the user performing a specific operation. However, since any function could be executed in the context of the application, an attacker could easily call a snippet of code that generates a valid nonce.
The plugin’s developers addressed the vulnerability shortly after being notified with the release of WordPress Download Manager 2.7.5. Users are advised to update their installations as soon as possible.
Over the past months, Sucuri has identified vulnerabilities in several popular WordPress plugins, including Slider Revolution, WP eCommerce, and Custom Contact Forms. Researchers have also discovered security holes in the platform itself. Last month, the Finland-based IT company Klikki Oy reported finding a critical cross-site scripting (XSS) vulnerability that affected close to 86% of WordPress installations (versions prior to 3.9.2).
Details on many WordPress vulnerabilities are available in the recently launched WordPress Vulnerability Database maintained by WPScan.