Arbitrary HTML injection vulnerability in ckeditor

Vulnerability

The vulnerability resides in the CKEditor 4 Clipboard package, affecting all users of CKEditor 4 versions >= 4.5.2. The bug allows an attacker to abuse the paste functionality by providing malformed HTML, which can result in injecting arbitrary HTML into the editor. The issue was patched in version 4.16.2 [1][2].

Exploitation

An attacker can exploit this vulnerability by crafting malformed HTML and triggering a paste operation in the CKEditor instance. The attacker does not need any special network position or authentication beyond the ability to submit content to the editor. The exploitation can be performed with user interaction (the user pastes the malformed content) or potentially automatically if the editor programmatically accepts pasted content from an untrusted source.

Impact

Successful exploitation allows an attacker to inject arbitrary HTML into the editor. This could lead to cross-site scripting (XSS) if the injected HTML includes JavaScript, or other client-side attacks depending on how the editor's output is processed. The attacker gains the ability to modify the content displayed to users, potentially leading to information disclosure or further compromise of the application.

Mitigation

The fix is available in CKEditor 4 version 4.16.2. Users should upgrade to this version or later. The open-source version of CKEditor 4 reached its End of Life on June 30, 2023, and no longer receives security updates; users are advised to upgrade to CKEditor 5 or consider the commercial CKEditor 4 LTS Extended Support Model for continued security patches until December 2028 [1].