The scenario suggests that only the employees who used the kiosks inside the building had their credentials compromised. Since the time-keeping website is accessible from the internet, it is possible that a malicious actor exploited an unpatched vulnerability in the site, allowing them to inject malicious code that captured the credentials of those who logged in from the kiosks. This is a common attack vector for stealing credentials from web applications.
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CompTIA Security+ SY0-701 Course Content: The course discusses web application vulnerabilities and how attackers can exploit them to steal credentials.