A public TTS host could 301/302/303-redirect POST /audio/speech to an internal
target (e.g. http://169.254.169.254), and urllib's default redirect handler
would follow it carrying the Authorization bearer — both an SSRF bounce past the
base-url guard and a credential leak. Now uses a no-redirect opener
(_NoRedirectTtsHandler raises on any redirect) via the _tts_open seam. +redirect
rejection regression test. Residual DNS-rebinding TOCTOU (re-resolve at connect)
is a narrower low-severity window noted for follow-up.
The base_url validator accepted any https host; an https URL pointing at an
internal/link-local/loopback/reserved IP (e.g. https://169.254.169.254 cloud
metadata, https://10.x internal) passed the scheme-only check. Now resolves the
host and rejects blocked-target addresses (private/loopback/link-local/reserved/
multicast/unspecified), while still allowing public OpenAI-compatible hosts and
the explicit localhost-over-http dev case. DNS-resolution failure is allowed
(unreachable host can't be an SSRF vector + avoids false-rejecting public hosts
that don't resolve in sandboxed envs). +5 regression vectors.
