CVE-2021-24439 in Browser Screenshots Plugin
Summary
by MITRE • 07/13/2021
The Browser Screenshots WordPress plugin before 1.7.6 allowed authenticated users with a role as low as Contributor to perform Stored Cross-Site Scripting attacks as the image_class parameter of the browser-shot shortcode was not escaped.
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Analysis
by VulDB Data Team • 07/15/2021
The vulnerability identified as CVE-2021-24439 resides within the Browser Screenshots WordPress plugin, a widely used tool for generating screenshots of web pages directly within the WordPress environment. This plugin enables users to capture and display screenshots of external websites or internal pages, making it a valuable feature for content creators and developers. However, the security flaw discovered in versions prior to 1.7.6 represents a critical oversight in input validation and output escaping mechanisms. The vulnerability specifically affects the image_class parameter within the browser-shot shortcode implementation, where user-supplied input fails to undergo proper sanitization before being rendered in the web page context. This oversight creates an avenue for malicious actors to inject arbitrary JavaScript code that executes in the context of other users' browsers, potentially compromising their sessions and data.
The technical nature of this vulnerability aligns with CWE-79, which describes Cross-Site Scripting (XSS) vulnerabilities occurring when untrusted data is incorporated into web pages without proper validation or escaping. In this case, the Contributor role user can exploit the flaw by crafting malicious input in the image_class parameter, which gets stored and later executed whenever the shortcode is rendered. The stored nature of this XSS attack means that the malicious payload persists in the database and affects all users who view the affected content, regardless of their role or authentication status. This particular vulnerability demonstrates a fundamental failure in the plugin's security architecture, where input validation occurs too late in the processing pipeline or not at all, allowing potentially dangerous content to be embedded within the plugin's output. The impact extends beyond simple script execution as it can enable session hijacking, data theft, and further exploitation through techniques such as credential harvesting or redirection to malicious sites.
The operational impact of CVE-2021-24439 is significant for WordPress installations utilizing the affected plugin version, as it provides attackers with a persistent means of executing malicious code against users with minimal privileges required. Contributors typically have limited capabilities within WordPress, including the ability to create and edit posts and pages, but this vulnerability allows them to escalate their privileges through indirect means. The stored XSS vulnerability creates a persistent threat where malicious scripts can be executed whenever any user views the affected content, potentially affecting administrators, editors, or other high-privilege users who may inadvertently encounter the compromised shortcode. This vulnerability also aligns with ATT&CK technique T1566, which covers social engineering tactics involving the delivery of malicious content through web-based applications. Organizations using the Browser Screenshots plugin without the security patch are exposed to risks including unauthorized access to sensitive data, potential compromise of administrative accounts, and the ability for attackers to establish persistent backdoors through the execution of malicious JavaScript code that can interact with the victim's browser environment.
The recommended mitigation for this vulnerability involves immediate upgrading to version 1.7.6 or later of the Browser Screenshots plugin, which implements proper input sanitization and output escaping for the image_class parameter. Additionally, administrators should implement proper input validation at multiple layers within their WordPress installations, ensuring that all user-supplied content undergoes rigorous sanitization before being stored or rendered. Network administrators should monitor for any suspicious activity related to the plugin, particularly around content creation and modification by users with Contributor roles or lower. Security teams should also consider implementing content security policies that restrict the execution of inline scripts and limit the potential impact of any successful XSS attacks. Organizations should conduct thorough security audits of their WordPress installations to identify other plugins or themes that may exhibit similar vulnerabilities in input handling and output escaping mechanisms. The incident highlights the critical importance of maintaining up-to-date software components and implementing robust security practices in web application development, particularly for plugins that handle user-generated content and execute within the context of authenticated sessions.