I discovered a stored cross-site scripting (XSS) vulnerability in a practice web application's comment section that allowed me to inject malicious JavaScript that would execute in any user's browser. By submitting a comment containing a script payload, I successfully stole session cookies from other users and could have hijacked their accounts, performed actions on their behalf, or defaced the website. This finding was documented in a comprehensive report including proof-of-concept screenshots showing cookie theft, CVSS risk scoring of 6.5 (Medium), and step-by-step remediation guidance including input sanitization and output encoding. This assessment demonstrates my ability to find client-side vulnerabilities that can compromise every user visiting the site.