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>

services/context/api.go

@@ -49,9 +49,10 @@ type APIContext struct {
 }
 
 // TokenCanAccessRepo reports whether the current API token is allowed to access the repository.
-// A public-only token cannot reach a private repo; any other token is unrestricted by this check.
+// A public-only token cannot reach a private repo or a repo owned by a non-public (limited or
+// private) owner; any other token is unrestricted by this check.
 func (ctx *APIContext) TokenCanAccessRepo(repo *repo_model.Repository) bool {
-	return repo == nil || !ctx.PublicOnly || !repo.IsPrivate
+	return !ctx.PublicOnly || !publicOnlyTokenDeniedRepo(ctx, repo)
 }
 
 func init() {

services/context/permission.go

@@ -4,6 +4,7 @@
 package context
 
 import (
+	"context"
 	"net/http"
 	"slices"
 
@@ -12,6 +13,39 @@ import (
 	"gitea.dev/models/unit"
 )
 
+// isOwnerHidden reports whether repo's owner is not publicly visible (a limited or private owner), so
+// the owner's repositories must be hidden from callers that may only reach genuinely public resources.
+func isOwnerHidden(ctx context.Context, repo *repo_model.Repository) bool {
+	if err := repo.LoadOwner(ctx); err != nil || repo.Owner == nil {
+		return true // fail closed if the owner visibility can't be determined
+	}
+	return !repo.Owner.Visibility.IsPublic()
+}
+
+// publicOnlyTokenDeniedRepo reports whether a public-only API token must be denied access to
+// repo. A public-only token may only reach genuinely public resources, so it is denied for
+// private repos and for repos owned by a non-public (limited or private) owner.
+func publicOnlyTokenDeniedRepo(ctx context.Context, repo *repo_model.Repository) bool {
+	if repo == nil {
+		return false
+	}
+	return repo.IsPrivate || isOwnerHidden(ctx, repo)
+}
+
+// TokenIsPublicOnly reports whether the request is authenticated by a public-only API token. A
+// non-token request, or a token with no recorded scope, is not public-only.
+func TokenIsPublicOnly(ctx *Context) bool {
+	if ctx.Data["IsApiToken"] != true {
+		return false
+	}
+	scope, ok := ctx.Data["ApiTokenScope"].(auth_model.AccessTokenScope)
+	if !ok {
+		return false
+	}
+	publicOnly, _ := scope.PublicOnly()
+	return publicOnly
+}
+
 // CheckTokenScopes checks whether the authenticated API token contains any of the given scopes.
 func CheckTokenScopes(ctx *Context, repo *repo_model.Repository, scopes ...auth_model.AccessTokenScope) {
 	if ctx.Data["IsApiToken"] != true {
@@ -29,7 +63,7 @@ func CheckTokenScopes(ctx *Context, repo *repo_model.Repository, scopes ...auth_
 		return
 	}
 
-	if publicOnly && repo != nil && repo.IsPrivate {
+	if publicOnly && publicOnlyTokenDeniedRepo(ctx, repo) {
 		ctx.HTTPError(http.StatusForbidden)
 		return
 	}