CVE-2025-59838 is a cross-site scripting (XSS) vulnerability identified in the Monkeytype typing test application, specifically affecting versions prior to commit f025b121cbe437e29de432b4aa72e0de22c755b7 (version 25.36.0 and earlier). Monkeytype is a minimalistic, customizable web-based typing test platform that allows users to load saved custom text for practice. The vulnerability arises from improper neutralization of user input during web page generation when loading these saved custom texts. Essentially, the application fails to adequately sanitize or encode user-supplied input before rendering it in the browser, enabling an attacker to inject malicious scripts. This can lead to execution of arbitrary JavaScript in the context of the victim's browser session. The vulnerability is classified under CWE-79, which covers improper input neutralization leading to XSS. The CVSS 4.0 base score is 2.4, indicating a low severity level, with the vector indicating local attack vector (AV:L), low attack complexity (AC:L), no privileges required (PR:L), user interaction required (UI:P), and limited scope impact (SI:L). No known exploits have been reported in the wild, and the issue has been patched in the referenced commit. The vulnerability primarily affects users who load saved custom texts, which implies that exploitation requires some user interaction and possibly some level of trust or social engineering to get a victim to load a maliciously crafted saved text. The impact is limited to the browser session and does not extend to server-side compromise or broader system integrity issues. The vulnerability does not affect confidentiality, integrity, or availability on a large scale but can be used for session hijacking, phishing, or other client-side attacks if exploited.

For European organizations, the impact of this vulnerability is generally low but not negligible. Monkeytype is a niche application used primarily for typing practice and is unlikely to be a critical business application. However, organizations that encourage or allow use of Monkeytype internally or have employees who use it on corporate devices could face risks related to session hijacking or credential theft if malicious scripts are executed. The vulnerability requires user interaction and local access to load malicious saved texts, limiting large-scale automated exploitation. Nonetheless, targeted attacks leveraging social engineering could exploit this vulnerability to compromise user sessions or steal sensitive information accessible via the browser. This could be particularly relevant in environments where employees use Monkeytype on browsers logged into corporate accounts or where browser-based single sign-on is in use. The low CVSS score reflects the limited scope and impact, but organizations should still consider the risk in the context of their threat model, especially if Monkeytype is used in training or educational settings within the organization.

To mitigate this vulnerability, European organizations should ensure that all instances of Monkeytype are updated to the patched version that includes commit f025b121cbe437e29de432b4aa72e0de22c755b7 or later. Since the vulnerability arises from improper input sanitization, applying the official patch is the most effective measure. Additionally, organizations should implement browser security best practices such as enabling Content Security Policy (CSP) headers to restrict script execution sources, which can help mitigate the impact of XSS vulnerabilities. User education is also important; users should be trained to avoid loading saved custom texts from untrusted sources and to be cautious about social engineering attempts that might trick them into loading malicious content. For environments where Monkeytype is used on corporate devices, restricting browser extensions and enforcing strict browser security configurations can reduce the risk of exploitation. Monitoring browser logs and network traffic for suspicious activity related to Monkeytype usage can provide early detection of attempted exploitation. Finally, organizations should consider isolating non-critical applications like Monkeytype from sensitive corporate environments to limit potential attack vectors.