Gitea: RSS/Atom feed handlers bypass API-token scope & public-only confinement (incomplete fix of #37698)

Summary

Gitea's RSS/Atom feed handlers accept API-token Basic auth but perform no token-scope or
public-only enforcement. A personal access token that is correctly blocked (HTTP 403) from a
private repository on /raw, /media, /archive, and /releases/download/... — because it is
marked public-only or lacks the repository scope category — still returns that repository's
private content through the feed routes. This is a token-confinement bypass and appears to be an
incomplete fix of #37698, which added that scope enforcement to the download handlers but not to the
sibling feed handlers.

This is not a cross-user access bug: the requesting account must still legitimately have repo
read access (RepoAssignment + reqUnitCodeReader are enforced). What is bypassed is the guarantee
that a confined token cannot reach private content — which is exactly the property #37698 was
shipped to provide for downloads, and which matters when such a token is handed to a third-party
service/CI, leaked, or used in a lower-trust integration.

Details

#37698 added context.CheckTokenScopes / CheckRepoScopedToken
(services/context/permission.go) to the raw / media / archive / attachment download handlers, so a
public-only or wrong-scope-category token cannot read private-repo content even when the owning user
otherwise has access.

The feed handlers are registered with webAuth.AllowBasic (so they accept token Basic auth) but call
no scope / public-only check. A grep for CheckTokenScopes / CheckRepoScopedToken / IsApiToken
across routers/web/feed/ and the release feed handlers returns nothing.

Affected routes (all token-reachable via webAuth.AllowBasic, none call the scope check):

Inconsistency that pins this down: the branch-feed routes sit in the same route group as /raw,
/media, /archive (all of which call checkDownloadTokenScope), and releases.rss sits next to
/releases/attachments/{uuid} and /releases/download/... (both go through ServeAttachment → scope
check). Only the feeds were missed. The API equivalents (ListReleases / ListTags) are scope-gated
via tokenRequiresScopes.

Two distinct confinement bypasses:

1. Public-only bypass. A token created with the public-only option is blocked (403) from a
   private repo on /raw, /archive, /releases/download/..., but returns private commit / release
   data via .../releases.rss, .../rss/branch/*, /{owner}/{repo}.rss, and the owner's private
   activity via /{user}.rss.
2. Scope-category bypass. A token scoped to only e.g. read:issue (no read:repository) is
   rejected by the download handlers but reads repository commit/release content via the feeds.

PoC

Verified live against the official gitea/gitea:1.26.2 Docker image (sqlite, feeds enabled).

Setup: non-admin user alice; private repo alice/secret with a commit
"SECRET-COMMIT-MARKER ..." (file secret.txt) and a release "Private Release" / body
"SECRET-RELEASE-MARKER ...". Two confined personal access tokens, both sent via HTTP Basic so the
auth method is identical across download and feed — only the route differs:

• Token A: scopes ["public-only", "read:repository"]
• Token B: scopes ["read:issue"]

 1# Token A — download is correctly blocked, feeds leak private content:
 2curl -u alice:$TOKEN_A https://<host>/alice/secret/raw/branch/main/secret.txt   # => 403  (fix works)
 3curl -u alice:$TOKEN_A https://<host>/alice/secret/rss/branch/main             # => 200, <title>SECRET-COMMIT-MARKER ...</title>
 4curl -u alice:$TOKEN_A https://<host>/alice/secret/releases.rss               # => 200, SECRET-RELEASE-MARKER ...
 5curl -u alice:$TOKEN_A "https://<host>/alice.rss"                             # => 200, private activity
 6 
 7# Token B — wrong scope category, same split:
 8curl -u alice:$TOKEN_B https://<host>/alice/secret/raw/branch/main/secret.txt   # => 403
 9curl -u alice:$TOKEN_B https://<host>/alice/secret/rss/branch/main             # => 200, private commit leaked

Anonymous baseline returns 404 on the repo feeds (data is genuinely private) and a marker-free 200 on
/alice.rss (public activity only) — confirming the leak is gated only by the missing token check.

Impact

Information disclosure of private commit metadata (SHA, message, author name+email),
release/tag notes, and the owner's private activity stream, to the holder of a confined token
that was specifically configured not to reach private content. Not raw file blobs (feeds don't
serve file contents). Requires a token belonging to an account that already has repo read access, so
the realistic threat is a leaked / shared / lower-trust token rather than an anonymous attacker —
which is precisely the threat model #37698 addressed for downloads.

Suggested remediation

Add a token-scope check at the top of each feed handler, mirroring checkDownloadTokenScope:

 1if context.CheckRepoScopedToken(ctx, ctx.Repo.Repository, auth_model.Read); ctx.Written() {
 2    return
 3}

for ShowBranchFeed, ShowRepoFeed, ShowFileFeed, ShowReleaseFeed (repo feeds). For the user
feed, gate includePrivate behind a non-public-only token (or require the user / repository
scope) so a confined token can't pull private activity.