## Description
Blocks `CONNECT` tunnels to private and reserved IP ranges in
aibridgeproxyd, preventing the proxy from being used to reach internal
networks.
The Coder access URL is always exempt (hostname+port match) so the proxy
can reach its own deployment. It is possible to exempt additional ranges
via `CODER_AIBRIDGE_PROXY_ALLOWED_PRIVATE_CIDRS`.
DNS rebinding is handled differently per path:
* Direct (no upstream proxy): validate the resolved IP right before the
TCP dial, no window between check and connect.
* Upstream proxy: Resolves and checks before forwarding to the upstream
dialer. A small rebinding window exists since the upstream proxy
re-resolves independently.
## Changes
* Add blocked IP denylist covering private, reserved, and
special-purpose ranges
* Add `AllowedPrivateCIDRs` option with CLI flag and env var
* Wire IP checks into `proxy.ConnectDial` for both upstream and direct
paths
* Add tests for blocked/allowed cases across direct dial, upstream
proxy, CIDR exemptions, and CoderAccessURL exemption
Notes: documentation will be handled in a follow-up PR.
Closes: https://github.com/coder/security/issues/124
Susana Ferreira
139594a4f4