Gitea: Fork-PR Actions task can read a third private repository via the collaborative-owner branch (missing fork-PR guard)
Summary
GetActionsUserRepoPermission (models/perm/access/repo_permission.go) decides whether an Actions
task token may access a target repo. Its cross-repo branches each enforce a fork-PR discriminator —
except the collaborative-owner branch, which is missing the !task.IsForkPullRequest guard that
its sibling has. As a result, when a private repo B lists owner A as a collaborative owner, an
attacker-controlled fork pull-request workflow whose base repo is owned by A is granted code-read
on B — i.e. the fork's YAML can clone a third private repository it has no rights to.
Details
// models/perm/access/repo_permission.go (v1.26.2), in GetActionsUserRepoPermission
if checkSameOwnerCrossRepoAccess(ctx, taskRepo, repo, task.IsForkPullRequest) { // passes isForkPR -> denies forks
return maxPerm, nil
}
...
if taskRepo.IsPrivate { // <-- NO IsForkPullRequest check here
actionsUnit := repo.MustGetUnit(ctx, unit.TypeActions)
if actionsUnit.ActionsConfig().IsCollaborativeOwner(taskRepo.OwnerID) {
return maxPerm, nil // grants code-read to target repo B
}
}The sibling same-owner path correctly denies fork PRs:
func checkSameOwnerCrossRepoAccess(ctx, taskRepo, targetRepo, isForkPR bool) bool {
if isForkPR {
return false // Fork PRs are never allowed cross-repo access to other private repositories.
}
...
}taskRepo = the repo whose workflow is running (the PR's base repo A); repo = the target being
cloned (B). IsCollaborativeOwner(taskRepo.OwnerID) asks "does target B's Actions config trust A's
owner for cross-repo read?" When B trusts ownerA, the branch returns maxPerm (code-read) **even when
task.IsForkPullRequest is true** — i.e. when the executing YAML is the fork's, not A's.
Every sibling enforces the fork-PR discriminator; except for this branch:
checkSameOwnerCrossRepoAccess denies forks; ComputeTaskTokenPermissions
(models/actions/token_permissions.go) only clamps the token *ceiling* to read-only for fork/cross-repo
(its own comment notes the access *decision* is in GetActionsUserRepoPermission, so it does not
neutralize the gap — it just makes the leak read-only); secrets (models/secret/secret.go) and the
approval gate (services/actions/notifier_helper.go) both correctly key on IsForkPullRequest.
Reachability — the runner clones target repo B over git-HTTP with the task token:
routers/web/repo/githttp.go → GetDoerRepoPermission(ctx, repoB, ActionsUser) →
GetActionsUserRepoPermission(ctx, repoB, actionsUser, taskID) with IsForkPullRequest == true →
collaborative-owner branch returns code-read → p.CanAccess(Read, code) passes → private clone of B
succeeds. (CheckRepoScopedToken in githttp is a no-op for the Actions token.)
PoC
Setup: private base repo A (usera/repoA), private third repo
B (userb/repoB) with a planted SECRET.txt, B's Actions config trusting usera as a collaborative
owner, and a genuine running fork-PR task token (token_hash computed with Gitea's own HashToken)
presented as HTTP Basic. Requesting GET /userb/repoB.git/info/refs?service=git-upload-pack:
| Condition (same fork-PR token) | HTTP | Meaning |
|---|---|---|
| anonymous (no token) | 401 | auth required |
| token, A public, B trusts A | 404 | branch gated on taskRepo.IsPrivate ⇒ A public skips it |
| token, A private, B has no collab-owner config | 404 | no trust ⇒ denied |
| token, A private, B trusts A (collab-owner) | 200 | git clone of private B succeeds |
| config removed / restored | 404 / 200 | deterministic |
In the 200 case, git clone of private repo B succeeded and yielded its SECRET.txt — the full source
of a third private repo the fork-PR author has no rights to.
Impact
Read-only confidentiality breach: discloses the full source of a *third* private repository (B) to an untrusted external fork-PR author. Read-only, not write/RCE.
Preconditions (honest):
- B is deliberately configured with a collaborative owner — but that is exactly the feature's intended
- The fork PR's base repo A is itself private (the branch is gated on
taskRepo.IsPrivate). Forking a
- The fork-PR workflow must actually run — most realistically via an attacker who had one earlier PR
ifNeedApproval), after which fork PRs auto-run.Suggested remediation
Add the same fork-PR guard the sibling path has (one line):
if taskRepo.IsPrivate && !task.IsForkPullRequest {
actionsUnit := repo.MustGetUnit(ctx, unit.TypeActions)
if actionsUnit.ActionsConfig().IsCollaborativeOwner(taskRepo.OwnerID) {
return maxPerm, nil
}
}This flips Vuln_ForkPR_LeaksThirdPrivateRepo to PASS, keeps Control_NonFork_Allowed PASS
(legitimate collaborative-owner sharing still works), and leaves the existing
TestGetActionsUserRepoPermission suite all green.