CVE-2024-8536 in Ultimate Blocks Plugin
Summary
by MITRE • 09/30/2024
The Ultimate Blocks WordPress plugin before 3.2.2 does not validate and escape some of its block attributes before outputting them back in a page/post where the block is embed, which could allow users with the contributor role and above to perform Stored Cross-Site Scripting attacks
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Analysis
by VulDB Data Team • 03/09/2025
The Ultimate Blocks WordPress plugin vulnerability CVE-2024-8536 represents a critical security flaw that enables stored cross-site scripting attacks through improper input validation and output escaping mechanisms. This vulnerability affects versions prior to 3.2.2 and specifically targets the plugin's handling of block attributes within WordPress pages and posts. The flaw occurs when the plugin fails to properly sanitize user-supplied data before rendering it back to the browser, creating an attack vector that can be exploited by users with contributor privileges and higher roles. The vulnerability stems from the plugin's insufficient validation of block attributes, which are parameters used to configure and display various content blocks within the WordPress editor environment.
The technical implementation of this vulnerability involves the plugin's failure to apply proper sanitization routines to block attribute values before they are stored in the database and subsequently rendered in the frontend output. When contributors or higher-privileged users create or modify content blocks containing malicious script payloads, these scripts are stored as part of the block configuration and executed whenever the page containing the block is loaded. This creates a persistent XSS attack vector where malicious code can be injected into the WordPress environment and executed in the context of other users' browsers. The vulnerability specifically impacts the plugin's block rendering system and its attribute handling mechanisms, which are designed to process user input for dynamic content generation.
From an operational perspective, this vulnerability poses significant risks to WordPress sites using the Ultimate Blocks plugin, particularly those with multiple contributors or users who can create content. The stored nature of the XSS attack means that malicious scripts persist in the database and can affect any user who views the affected pages, potentially leading to session hijacking, credential theft, or further exploitation of the compromised systems. Attackers can leverage this vulnerability to execute arbitrary JavaScript code in the browsers of other users, potentially gaining access to sensitive information or performing unauthorized actions within the WordPress administration interface. The impact extends beyond simple script execution as it can be used to establish persistent backdoors or facilitate more sophisticated attacks against the entire WordPress installation.
The vulnerability aligns with CWE-79 which defines Cross-Site Scripting as a common weakness in web applications where untrusted data is improperly incorporated into web pages. It also maps to ATT&CK technique T1059.007 for Command and Scripting Interpreter: JavaScript, as the exploitation involves JavaScript code execution. The attack surface is particularly concerning given that contributors typically have limited capabilities but can now escalate their privileges through stored XSS. Security practitioners should prioritize patching this vulnerability immediately, as it can be exploited by users who should not have the ability to inject malicious scripts into the site. The remediation approach involves updating to version 3.2.2 or later, which includes proper input validation and output escaping mechanisms that prevent the injection of malicious code into block attributes. Organizations should also implement additional security measures such as content security policies, regular security audits, and monitoring for suspicious content creation activities to further mitigate potential risks associated with this vulnerability.