SSRF via first-party proxy -- no target domain allowlist

[aram356]

Summary

The /first-party/proxy endpoint proxies to arbitrary URLs (protected only by tstoken signature). proxy_with_redirects follows up to 4 redirects with no domain or IP range restriction, allowing SSRF to internal services if a signed URL redirects.

Refs

• crates/common/src/proxy.rs lines 600-621 — handle_first_party_proxy
• crates/common/src/proxy.rs lines 463-582 — proxy_with_redirects follows redirects

Recommendation

Validate redirect targets against an allowlist or block private IP ranges.

Context

Production readiness audit — see #396