Gitea: API access token scope enforcement bypass on repository RSS/Atom feed endpoints leaks private repository commit data

Summary

A Gitea personal access token (PAT) restricted to a non-repository scope (e.g. read:issue) can read the commit history of any private repository the token owner can access, via the repository RSS/Atom feed endpoints. The same token is correctly denied (403) on /raw, /media, /archive, and the contents API. It leaks commit SHAs, full commit messages (which frequently contain secrets and internal context), and committer name + email.

Details

Gitea enforces PAT scope on repository-content endpoints via checkDownloadTokenScope() (added in PR #37698, extended to the archive endpoint by the CVE-2026-20706 fix in 1.26.2). The RSS/Atom feed handlers were never included: they (a) opt into PAT auth via webAuth.AllowBasic, (b) serve private-repo content, but (c) never call checkDownloadTokenScope().

Affected handlers (all carry AllowBasic, none call the scope check):

• RenderBranchFeedRSS/Atom - routers/web/feed/render.go (last 10 commits: SHA, title, full message, committer name + email)
• ShowFileFeed - routers/web/feed/file.go (per-file commit history)
• repo activity feed /{owner}/{repo}.rss / .atom
• TagsListFeedRSS/Atom, ReleasesFeedRSS/Atom - routers/web/repo/release.go

Root cause: routers/web/web.go registers the feed routes with webAuth.AllowBasic so a PAT authenticates, but the unit-permission middleware only checks the user's access, not the token's scope. checkDownloadTokenScope (routers/web/repo/download.go and the archive Download in repo.go) exists to close exactly that gap and is absent from the feed handlers. Same class as the recently fixed download/archive bypasses (GHSA-cr4g-f395-h25h / CVE-2026-20706); the feeds are the surface those fixes missed.

PoC

Tested on gitea/gitea:1.26.2-rootless, confirmed present at main HEAD (9608cc2, 2026-06-13).

1. User carol owns private repo carol/priv with a commit (message: "add confidential secret").
2. Create a PAT scoped to issues only, no repository scope:
   curl -u carol:PASS -X POST $HOST/api/v1/users/carol/tokens -d '{"name":"t","scopes":["read:issue"]}'
3. Scope-enforcing sibling correctly denies it:
   curl -u carol:$TOK $HOST/carol/priv/raw/branch/main/secret.txt -> 403
4. The feed leaks private data with the same token:
   curl -u carol:$TOK $HOST/carol/priv/rss/branch/main -> 200, returns
   <description>add confidential secret ... this commit message itself is sensitive</description>

Impact

PATs are routinely issued narrowly and handed to third-party bots, CI jobs, or chat integrations that are meant to have no code access. This bypass lets such a token exfiltrate private-repository commit history (messages often hold secrets, ticket refs, internal context) and committer emails for every repository the owner can read. Confidentiality only; no integrity or availability impact. Preconditions: a valid PAT of any non-repository scope owned by a user with read access to the target private repo, and feeds enabled (Other.EnableFeed, default ON).

Suggested fix: call checkDownloadTokenScope(ctx) at the start of each feed handler (mirroring download.go). Longer-term, enforce repository token scope in a single route-group middleware wherever AllowBasic / AllowOAuth2 is set on a repo-content route, so the next added endpoint cannot miss it.