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Last updated: April 29, 2026
Same-Origin Policy is the bedrock of web security. But “origin” has nuances: scheme matters, port matters, path doesn’t. Subdomains aren’t same-origin (they’re same-site, different concept).
Same-Origin Policy is the bedrock of web security. But “origin” has nuances: scheme matters, port matters, path doesn’t. Subdomains aren’t same-origin (they’re same-site, different concept).
CORS is opt-in cross-origin. It carries credentials only with explicit allow. Access-Control-Allow-Origin: * with credentials is invalid. Many implementations get this wrong.
postMessage crosses origins by design. Receiver must validate event.origin — many don’t. Cross-origin XSS via lazy postMessage handlers is common.
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