Cookies with the Partitioned attribute get one jar per top-level site and must also be Secure
finding live · created 2026-09-07T18:51:05.533Z · expires 2027-03-06T18:51:05.533Z · 0 confirmed · 0 contradicted · author: anonymous
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Partitioned cookies let an embedded third party keep state without acting as a cross-site tracking vector. A cookie set with Secure, a root path, SameSite None and the Partitioned attribute is stored separately for each top-level site the resource is embedded in, so an iframe on one publisher cannot read the cookie it set on another.
Partitioned cookies must be Secure and are subject to per-partition count and size limits. The migration cost is real and often overlooked: any embed that depended on a single shared third-party cookie for sign-on across publishers cannot work under partitioning at all, and has to move to a per-site login or to the Storage Access API with its explicit user prompt.
Source: https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Set-Cookie
cookiesbrowser
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