CVE-2021-24208 in WP Page Builder Plugin
Summary
by MITRE • 04/06/2021
The editor of the WP Page Builder WordPress plugin before 1.2.4 allows lower-privileged users to insert unfiltered HTML, including JavaScript, into pages via the “Raw HTML” widget and the “Custom HTML” widgets (though the custom HTML widget requires sending a crafted request - it appears that this widget uses some form of client side validation but not server side validation), all of which are added via the “page_builder_data” parameter when performing the “wppb_page_save” AJAX action. It is also possible to insert malicious JavaScript via the “wppb_page_css” parameter (this can be done by closing out the style tag and opening a script tag) when performing the “wppb_page_save” AJAX action.
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Analysis
by VulDB Data Team • 04/10/2021
The vulnerability identified as CVE-2021-24208 affects the WP Page Builder WordPress plugin version 1.2.3 and earlier, representing a critical security flaw that undermines the plugin's input validation mechanisms. This weakness allows users with lower privileges to bypass standard content filtering procedures and inject arbitrary HTML code including potentially malicious JavaScript directly into WordPress pages through specific widgets. The vulnerability specifically targets the Raw HTML and Custom HTML widgets within the plugin's interface, where user input is processed without adequate server-side sanitization. The attack vector operates through the wppb_page_save AJAX action, which handles page building data submissions, making it accessible to unauthorized users who can manipulate the page_builder_data parameter to execute malicious payloads.
The technical implementation of this vulnerability stems from inadequate server-side validation of user-supplied content within the page builder functionality. When users submit content through the Raw HTML widget, the system fails to properly sanitize the input before storing it in the WordPress database, creating a persistent cross-site scripting (XSS) vulnerability. The Custom HTML widget presents a similar risk but requires a more sophisticated attack approach involving crafted requests that exploit client-side validation bypasses. The vulnerability also extends to the wppb_page_css parameter, where attackers can manipulate CSS stylesheets by closing existing style tags and injecting script tags, effectively circumventing standard security measures. This multi-vector approach increases the attack surface and makes the vulnerability particularly dangerous as it can be exploited through multiple pathways within the same plugin functionality.
The operational impact of CVE-2021-24208 extends beyond simple XSS exploitation to potentially enable full administrative compromise of affected WordPress installations. Lower-privileged users who can access the page builder interface can leverage this vulnerability to inject JavaScript code that executes in the context of other users' browsers, potentially stealing session cookies, performing unauthorized actions, or redirecting users to malicious sites. The vulnerability's persistence through the page_builder_data parameter means that injected code remains active until manually removed, creating long-term exposure windows. Additionally, the ability to manipulate CSS through the wppb_page_css parameter allows attackers to craft more sophisticated attacks, including CSS-based phishing attempts or additional JavaScript injection vectors that can be leveraged for privilege escalation or data exfiltration.
Organizations affected by this vulnerability should prioritize immediate remediation through updating to WP Page Builder version 1.2.4 or later, which includes proper input sanitization and server-side validation controls. The mitigation strategy should also include implementing additional security layers such as content security policies to limit script execution and monitoring for unauthorized content modifications. Security teams should conduct thorough audits of all page builder and content management plugins to identify similar validation gaps, as this vulnerability aligns with CWE-79 (Cross-site Scripting) and CWE-20 (Improper Input Validation) categories. The ATT&CK framework categorizes this vulnerability under T1059.007 (Command and Scripting Interpreter: JavaScript) and T1566.001 (Phishing: Spearphishing Attachment), highlighting the potential for automated exploitation and social engineering attacks. Regular security scanning and vulnerability assessments should be implemented to detect similar weaknesses in other WordPress plugins, particularly those handling user-generated content or providing rich text editing capabilities, as the underlying architectural flaw represents a common pattern in web application development that requires comprehensive input validation across all user-facing interfaces.