Gitea private attachment disclosure through repository mismatch

Gitea's web attachment handler skips its cross-repository ownership check for attachments created before 16 January 2026 and checks permissions against the repository named in the request URL instead. An unauthenticated attacker who knows a private attachment's UUID can request it through a public repository's attachment path and retrieve its contents. This can expose issue and pull request attachments or release assets; the random attachment UUID must already be known to the attacker.