Overview
CVE-2025-66563 describes a cross-site scripting (XSS) vulnerability found in Monkeytype, a popular minimalistic and customizable typing test application. Specifically, versions 25.49.0 and earlier are affected. The vulnerability stems from improper handling of user-supplied input within quote submissions. An attacker can leverage this flaw to inject and execute malicious JavaScript code on the browsers of other users viewing the crafted quote.
Technical Details
The core of the vulnerability lies in how Monkeytype handles the quote.text and quote.source fields when users submit quotes. These fields, which are meant to contain the text of the quote and its source, respectively, are directly inserted into the Document Object Model (DOM) without proper sanitization. While some escaping is performed using quotes and textarea tags, it’s insufficient to prevent the injection of malicious HTML and JavaScript.
An attacker can craft a malicious quote submission that contains HTML tags and JavaScript code within the quote.text or quote.source fields. When another user views this quote, the injected HTML and JavaScript will be rendered and executed in their browser context, potentially leading to account compromise, data theft, or other malicious actions.
CVSS Analysis
Due to the nature of this vulnerability, a CVSS score would typically be assigned. However, the provided information indicates “N/A” for both Severity and CVSS Score. A likely estimated CVSS score would be between 6.1 and 7.5 (Medium to High) because of the potential for malicious Javascript Execution and user compromise.
Possible Impact
The exploitation of this XSS vulnerability can have significant consequences:
- Account Takeover: An attacker could steal user cookies or session tokens, leading to account compromise.
- Data Theft: Malicious JavaScript can be used to extract sensitive information from the user’s browser, such as personal data, browsing history, or financial information.
- Redirection to Malicious Sites: Users could be redirected to phishing websites or other malicious domains without their knowledge.
- Defacement: The attacker could modify the content displayed on the Monkeytype page for other users.
Mitigation or Patch Steps
The vulnerability has been addressed in a subsequent commit. Users of Monkeytype versions 25.49.0 and earlier are strongly advised to update to a patched version. If upgrading isn’t immediately feasible, consider implementing input validation and sanitization on the server-side to prevent the injection of malicious HTML and JavaScript. However, updating to the latest version is the recommended approach.
