Lab: Same Site Strict bypass via client-side redirect
Summary: PortSwigger's lab demonstrates a CSRF attack that bypasses SameSite=Strict session cookies by abusing a client-side redirect: the comment confirmation page's JavaScript builds a redirect path from the postId query parameter, and a path traversal sequence in that parameter sends the browser to an arbitrary endpoint on the target site. Because the redirect originates from the target's own domain, the browser attaches the Strict session cookie to the follow-up request, and the change-email endpoint accepts the change via GET, letting the exploit server alter the victim's email address.
Key Takeaway: A SameSite=Strict cookie is often treated as sufficient CSRF protection, but here a single client-side redirect built from an unvalidated query parameter re-establishes the authenticated context the attacker needs - and the change-email endpoint accepting GET removes the last barrier.
Read the original at PortSwigger Research ↗
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