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Cross-Site Scripting (XSS) is a web application attack where an attacker injects malicious client-side scripts into trusted websites that are then executed in a user’s browser. It exploits improper input validation and output encoding rather than flaws in the browser itself.
How is Cross-Site Scripting abused
Attackers inject malicious JavaScript through input fields, URLs, or stored content that a web application fails to sanitize. When a victim loads the affected page, the script executes in the context of the trusted site, allowing attackers to steal session cookies, capture credentials, manipulate page content, or perform actions on behalf of the user.
Why Cross-Site Scripting matters
Cross-Site Scripting enables attackers to hijack authenticated user sessions without breaching the server. A successful XSS attack can lead to account takeover, unauthorized transactions, data theft, or serve as a stepping stone for broader compromise of enterprise web applications.
Real-world example
In late 2025, the U.S. Cybersecurity and Infrastructure Security Agency (CISA) added an actively exploited cross-site scripting (XSS) vulnerability — CVE-2021-26829 — in the OpenPLC ScadaBR industrial control system to its Known Exploited Vulnerabilities (KEV) catalog. Threat activity associated with this flaw included web-based script injection that allowed attackers to manipulate the system’s web interface, demonstrating live exploitation of XSS in operational technology environments. Security teams were urged to patch and mitigate by December 2025 due to confirmed exploitation in the wild.
Source
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Additional Resources
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