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Vulnerability record · CVE-2025-66563 · published 4 December 2025

CVE-2025-66563: Monkeytype cross-site scripting vulnerability

Monkeytype · Monkeytype

Monkeytype is a minimalistic and customizable typing test. In 25.49.0 and earlier, there is improper handling of user input which allows an attacker to execute malicious javascript on anyone viewing a malicious quote submission. quote.text and quote.source are user input, and they're inserted straight into the DOM. If they contain HTML tags, they will be rendered (after some escaping using quotes and textarea tags).

7.1 CVSS 4.0 High EPSS 0.24% · top 86.6% CWE-79 · Cross-site scripting
7.1CVSS 4.0 base score
0.24%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
3References, 2 tagged exploit
17 Jun 2026Last modified by NVD

Description

Monkeytype is a minimalistic and customizable typing test. In 25.49.0 and earlier, there is improper handling of user input which allows an attacker to execute malicious javascript on anyone viewing a malicious quote submission. quote.text and quote.source are user input, and they're inserted straight into the DOM. If they contain HTML tags, they will be rendered (after some escaping using quotes and textarea tags).

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/monkeytypegame/monkeytype/commit/d6d062a77132ba7d6ba3b482d46ae329d3b8d695 Patch
https://github.com/monkeytypegame/monkeytype/security/advisories/GHSA-mfjh-9552-8g27 ExploitVendor Advisory
https://github.com/monkeytypegame/monkeytype/security/advisories/GHSA-mfjh-9552-8g27 ExploitVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2025-66563), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.