CVE-2023-48219: TinyMCE Editor Vulnerable to Mutation Cross-Site Scripting Attack

In the world of web development, rich text editors (RTEs) play a crucial role in allowing users to create and edit content without requiring extensive HTML knowledge. TinyMCE, one of the most popular RTEs, has recently been found vulnerable to a mutation cross-site scripting (mXSS) attack. The CVE-2023-48219 vulnerability, if exploited, could allow attackers to inject malicious code into websites and potentially compromise user data.

What is mXSS?

mXSS is a type of cross-site scripting (XSS) attack that exploits the way data is processed within an application, such as during sanitization or serialization. Unlike traditional XSS attacks that rely on injecting malicious code directly into an application’s input fields, mXSS attacks involve modifying existing data within the application to trigger XSS vulnerabilities.

The TinyMCE Vulnerability

The mXSS vulnerability in TinyMCE affects the editor’s core undo/redo functionality and other APIs and plugins. Text nodes within specific parent elements are not properly escaped during serialization, making them susceptible to manipulation. Attackers can exploit this vulnerability by crafting malicious snippets of HTML code that contain special characters reserved as internal markers. These markers are initially ignored by the editor’s sanitization layer, but they can be reactivated when the content is processed for undo/redo operations or when using specific APIs and plugins.

The discovery of the CVE-2023-48219 vulnerability is credited to Masato Kinugawa of Cure53, who responsibly disclosed the issue to TinyMCE developers.

Impact of the Vulnerability

If exploited, this vulnerability could allow attackers to inject malicious JavaScript code into websites, potentially leading to various consequences, such as:

• Stealing user credentials: Attackers could steal sensitive information, such as login credentials, cookies, and other session data.
• Redirecting users to malicious websites: Attackers could redirect users to phishing websites or websites that distribute malware.
• Defacing websites: Attackers could alter the content of websites, injecting their messages or propaganda.

Remediation

TinyMCE has addressed this vulnerability in TinyMCE 6.7.3 and TinyMCE 5.10.9. To protect your websites from this vulnerability, it is recommended to upgrade to these versions or later. Additionally, developers should exercise caution when using the affected APIs and plugins, ensuring that all user-provided content is properly sanitized.