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: → → with → collaborative-owner branch returns code-read → passes → private clone of B succeeds. ( in githttp is a no-op for the Actions token.)