fix: various security fixes (#38406)

Addresses a batch of privately reported security issues, grouped by
area:

- **SSRF** - migration PR-patch/asset fetches, OAuth2 avatar & OpenID
discovery, pull-mirror URL re-validation, and the outbound proxy path.
- **Access-token scope** - prevent scope escalation on token creation;
keep public-only tokens confined (feeds, packages, Actions listings,
star/watch lists, limited/private owners).
- **Access control / disclosure** - go-get default-branch leak, webhook
authorization-header leak, watch clearing on private transitions,
label/attachment scoping.
- **Denial of service** - input bounds for npm dist-tags, Debian control
files, Arch file lists, and SSH keys.

### 📌 Attention for site admins

Not breaking - existing configs keep working - but two changes are worth
a look:

- **New SSRF protection** Outbound requests (migrations, OAuth2 avatars,
OpenID discovery, pull mirrors, proxy path) are now validated against
the allow/block host lists. If your instance legitimately reaches
internal hosts, you may need to add them to
`[security].ALLOWED_HOST_LIST` (and the relevant `ALLOW_LOCALNETWORKS`
settings).
- **Deprecation** `[webhook].ALLOWED_HOST_LIST` is deprecated and will
be removed in a future release. Use `[security].ALLOWED_HOST_LIST`
instead; the old key still works for now.

---------

Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>

tests/integration/mirror_pull_test.go

@@ -4,7 +4,10 @@
 package integration
 
 import (
+	"net/http"
+	"net/http/httptest"
 	"slices"
+	"sync/atomic"
 	"testing"
 
 	"gitea.dev/models/db"
@@ -14,6 +17,9 @@ import (
 	user_model "gitea.dev/models/user"
 	"gitea.dev/modules/gitrepo"
 	"gitea.dev/modules/migration"
+	"gitea.dev/modules/setting"
+	"gitea.dev/modules/test"
+	migrations "gitea.dev/services/migrations"
 	mirror_service "gitea.dev/services/mirror"
 	release_service "gitea.dev/services/release"
 	repo_service "gitea.dev/services/repository"
@@ -124,3 +130,48 @@ func TestMirrorPull(t *testing.T) {
 	mirror = unittest.AssertExistsAndLoadBean(t, &repo_model.Mirror{RepoID: mirrorRepo.ID})
 	assert.Equal(t, lastMirrorSync, mirror.LastSyncUnix)
 }
+
+// TestMirrorPullSSRFRevalidation ensures a pull mirror re-validates its remote URL against
+// the migration allow/block list on every sync, so a mirror whose (network) remote now
+// points at a disallowed internal host is never fetched.
+func TestMirrorPullSSRFRevalidation(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	ctx := t.Context()
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+	repoPath := repo_model.RepoPath(user.Name, repo.Name)
+
+	// an "internal" server that records whether it was reached
+	var reached atomic.Bool
+	internal := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		reached.Store(true)
+		w.WriteHeader(http.StatusNotFound)
+	}))
+	defer internal.Close()
+
+	mirrorRepo, err := repo_service.CreateRepositoryDirectly(ctx, user, user, repo_service.CreateRepoOptions{
+		Name:     "ssrf_mirror",
+		IsMirror: true,
+		Status:   repo_model.RepositoryBeingMigrated,
+	}, false)
+	require.NoError(t, err)
+	_, err = repo_service.MigrateRepositoryGitData(ctx, user, mirrorRepo, migration.MigrateOptions{
+		RepoName:  "ssrf_mirror",
+		Mirror:    true,
+		CloneAddr: repoPath,
+	}, nil)
+	require.NoError(t, err)
+
+	mirror, err := repo_model.GetMirrorByRepoID(ctx, mirrorRepo.ID)
+	require.NoError(t, err)
+
+	// repoint the mirror at the loopback server, which is disallowed once local networks are off
+	require.NoError(t, mirror_service.UpdateAddress(ctx, mirror, internal.URL+"/repo.git"))
+	defer test.MockVariableValue(&setting.Migrations.AllowLocalNetworks, false)()
+	require.NoError(t, migrations.Init())
+	t.Cleanup(func() { _ = migrations.Init() })
+
+	assert.False(t, mirror_service.SyncPullMirror(ctx, mirrorRepo.ID))
+	assert.False(t, reached.Load(), "the disallowed internal remote must not be reached")
+}