Gitea: OAuth2 access token scope enforcement bypass via HTTP Basic authentication

Summary

Gitea fails to enforce OAuth2 access token scopes when the token is submitted via HTTP Basic authentication instead of a Bearer token. An OAuth2 application granted only read:user can use the same token as Authorization: Basic base64(<token>:x-oauth-basic) and perform write actions, including modifying profiles, adding email addresses, creating repositories, and deleting repositories as the authorizing user.

Details

Root cause: services/auth/basic.go accepts OAuth2 access tokens through the Basic auth path but does not store the token scope in the request context:

// services/auth/basic.go
if uid != 0 {
    store.GetData()["LoginMethod"] = OAuth2TokenMethodName
    store.GetData()["IsApiToken"] = true   // scope is NOT set
    return u, nil
}

The scope enforcement middleware in routers/api/v1/api.go exits early when ApiTokenScope is absent:

// routers/api/v1/api.go — tokenRequiresScopes
scope, scopeExists := ctx.Data["ApiTokenScope"].(auth_model.AccessTokenScope)
if ctx.Data["IsApiToken"] != true || !scopeExists {
    return   //<- exits without checking scope, all actions permitted
}

When a token arrives via Bearer, ApiTokenScope is populated and scope checks apply normally. When the same token arrives via Basic auth, ApiTokenScope is never set, so tokenRequiresScopes returns immediately and no scope is enforced.

Suggested fix: When an OAuth2 access token is accepted in services/auth/basic.go, populate ApiTokenScope in the request context identically to the Bearer-token OAuth2 path.

PoC

1. Create an OAuth2 application in Gitea.
2. Authorize it as a normal user with scope read:user only.
3. Take the resulting access token and call a write endpoint both ways:

Bearer | correctly blocked:

Authorization: Bearer <token>
PATCH /api/v1/user/settings  ->  403 Forbidden

Basic | bypass: