CVE-2021-32809 in CKEditor
Summary
by MITRE • 08/12/2021
ckeditor is an open source WYSIWYG HTML editor with rich content support. A potential vulnerability has been discovered in CKEditor 4 [Clipboard](https://ckeditor.com/cke4/addon/clipboard) package. The vulnerability allowed to abuse paste functionality using malformed HTML, which could result in injecting arbitrary HTML into the editor. It affects all users using the CKEditor 4 plugins listed above at version >= 4.5.2. 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-2021-32809 resides within the CKEditor 4 clipboard package, specifically targeting the paste functionality that enables users to insert content from external sources into the rich text editor environment. This issue represents a critical security flaw that could be exploited by malicious actors to inject arbitrary HTML code into the editor, potentially compromising the integrity of content management systems that rely on CKEditor 4 for user-generated content processing. The vulnerability affects all implementations using CKEditor 4 versions 4.5.2 and above, making it a widespread concern across numerous web applications that utilize this popular open source WYSIWYG editor. The attack vector leverages malformed HTML content that, when pasted into the editor, bypasses normal sanitization mechanisms and executes unintended code injection operations.
The technical exploitation of this vulnerability occurs through the clipboard package's handling of pasted content, where the editor fails to properly sanitize or validate HTML fragments that contain malicious payloads. This flaw allows attackers to craft specially formatted HTML content that, when pasted into the CKEditor interface, gets processed and rendered within the editor environment without adequate security controls. The underlying issue stems from insufficient input validation and sanitization within the clipboard processing pipeline, which permits potentially harmful HTML elements to pass through the system's security filters. This vulnerability directly maps to CWE-79, which describes Cross-Site Scripting (XSS) conditions where untrusted data is improperly handled and executed within a web application context. The vulnerability's impact extends beyond simple content modification, as it can potentially enable more sophisticated attacks including session hijacking, data exfiltration, or the execution of malicious scripts in the context of the victim's browser session.
The operational impact of CVE-2021-32809 poses significant risks to organizations that depend on CKEditor 4 for content management, user-generated content systems, or collaborative platforms where users can submit HTML content. Attackers could exploit this vulnerability to inject malicious scripts that would execute in the browser context of other users viewing the affected content, creating a potential attack surface for cross-site scripting campaigns. This vulnerability particularly threatens web applications that do not implement additional content filtering or sanitization layers beyond the editor itself, as the malicious code injection could occur silently during normal user operations. The attack chain typically involves preparing malicious HTML content, pasting it into the CKEditor interface, and then having the injected code execute when the content is rendered or processed by other users. Organizations using CKEditor 4 in production environments face potential data breaches, service disruption, and reputational damage if this vulnerability is not addressed through proper patch management protocols.
The remediation for CVE-2021-32809 requires immediate implementation of the official patch available in CKEditor 4.16.2, which addresses the clipboard package's insufficient sanitization mechanisms. Organizations should prioritize updating their CKEditor 4 installations to version 4.16.2 or later to ensure protection against this vulnerability. Additionally, administrators should consider implementing additional security measures such as content security policies, enhanced input validation at application level, and regular security audits of web applications that utilize CKEditor 4. The vulnerability's classification under the ATT&CK framework would fall under the T1059.008 technique for 'Command and Scripting Interpreter: PowerShell' and potentially T1566.001 for 'Phishing: Spearphishing Attachment' when considering the broader attack surface that this vulnerability could enable. Organizations should also implement monitoring and logging of clipboard operations within their applications to detect potential exploitation attempts and establish incident response procedures for handling such security events. The patch resolution addresses the core issue by strengthening the HTML sanitization process within the clipboard package, ensuring that malformed or potentially malicious content is properly filtered before being processed by the editor's core functionality.