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A visitor with no cookie who opened someone else's `?owner=` link took that uid as the first entry of their list, and the form insert files new pastes under the first entry. Everything the visitor created afterwards therefore belonged to whoever handed out the link, who could delete it. Mint an own uid before appending the claim, so a claim only ever grants rights over the pastes it came with. The handoff is also GET-only now. A cross-site POST does not carry the `SameSite=Lax` uid cookie, so honouring it there let an attacker page auto-submit a hidden form and set a cookie over the visitor's real one, costing them the right to delete everything they had made. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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A visitor with no cookie who opened someone else's
?owner=link took that uid as the first entry of their list, and the form insert files new pastes under the first entry. Everything the visitor created afterwards therefore belonged to whoever handed out the link, who could delete it. Mint an own uid before appending the claim, so a claim only ever grants rights over the pastes it came with.The handoff is also GET-only now. A cross-site POST does not carry the
SameSite=Laxuid cookie, so honouring it there let an attacker page auto-submit a hidden form and set a cookie over the visitor's real one, costing them the right to delete everything they had made.