CVE-2021-32808 in CKEditor
Summary
by MITRE • 08/12/2021
ckeditor is an open source WYSIWYG HTML editor with rich content support. A vulnerability has been discovered in the clipboard Widget plugin if used alongside the undo feature. The vulnerability allows a user to abuse undo functionality using malformed widget HTML, which could result in executing JavaScript code. It affects all users using the CKEditor 4 plugins listed above at version >= 4.13.0. The problem has been recognized and patched. The fix will be available in version 4.16.2.
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Analysis
by VulDB Data Team • 08/18/2021
The vulnerability identified as CVE-2021-32808 resides within the CKEditor 4 clipboard widget plugin, specifically when utilized in conjunction with the undo feature. This represents a critical security flaw that exploits the interaction between two core editor functionalities to enable arbitrary code execution. The issue affects all CKEditor 4 implementations that have version 4.13.0 or higher, making it a widespread concern across numerous web applications that rely on this popular WYSIWYG editor for content management. The vulnerability stems from inadequate input validation and sanitization mechanisms within the widget processing pipeline, particularly when handling clipboard data that contains malformed HTML structures.
The technical exploitation occurs through a carefully crafted malicious HTML payload that leverages the undo functionality to execute JavaScript code within the victim's browser context. When a user performs an undo operation on a malformed widget HTML structure, the editor's processing logic fails to properly sanitize the input before reprocessing it, creating a code execution vector. This flaw operates under the CWE-79 principle of Cross-Site Scripting, specifically manifesting as a client-side code injection vulnerability that bypasses normal security boundaries. The attack requires minimal user interaction, as the malicious code executes automatically during the undo operation, making it particularly dangerous in environments where users may unknowingly trigger the exploit through clipboard operations.
The operational impact of this vulnerability extends beyond simple code execution, as it can lead to complete browser compromise and potential data exfiltration. Attackers can leverage this vulnerability to inject malicious scripts that can steal session cookies, redirect users to malicious sites, or perform other harmful actions within the context of the vulnerable web application. The vulnerability affects web applications that use CKEditor 4 in their content management systems, rich text editors, or any platform that relies on the clipboard widget functionality. Given that CKEditor 4 is widely deployed across numerous content management systems, enterprise applications, and web platforms, the potential attack surface is extensive. The vulnerability can be exploited through various attack vectors including email attachments, web forms, or any mechanism that allows clipboard data to be processed by the editor.
Mitigation strategies for CVE-2021-32808 primarily involve upgrading to CKEditor 4.16.2 or later versions where the fix has been implemented. Organizations should conduct immediate vulnerability assessments to identify all systems running affected CKEditor versions and prioritize patching efforts. Additionally, implementing Content Security Policy headers can provide an additional layer of protection against potential exploitation attempts. Security teams should also consider monitoring for suspicious clipboard operations and implementing input validation measures at the application level. The fix addresses the core issue by properly sanitizing widget HTML structures during undo operations and ensuring that malformed content cannot trigger JavaScript execution. Organizations should also review their web application security configurations and consider implementing web application firewalls to detect and block potential exploitation attempts. This vulnerability highlights the importance of thorough input validation and the potential risks introduced by complex editor functionalities that process user-generated content through multiple processing stages.