Security: bind services to loopback with Host + CORS allowlists #1

2026-08-07T14:50:10Z

Athena commented

2026-08-07 14:50:10 +00:00

Summary

The Synapse backend and memory service bound 0.0.0.0 with wildcard CORS and no auth, exposing the full unauthenticated admin/data API to the LAN. This PR:

Defaults the uvicorn bind to 127.0.0.1 (NEXUS_BIND_HOST override) in management/ncp.py.
Scopes CORS to known local origins instead of * on both the backend and the memory service.
Adds TrustedHostMiddleware to reject foreign Host headers, which defeats DNS-rebinding — something same-origin CORS cannot stop.

NEXUS_ALLOWED_HOSTS / NEXUS_ALLOWED_ORIGINS allow opt-in LAN exposure, intended to be paired with real authentication.

Testing

Verified services listen only on 127.0.0.1 after the change.
Probed endpoints with foreign Origin and Host headers: foreign hosts get 400, CORS preflight only allows the local-origin allowlist.
pytest smoke tests pass.

Stack note

This is PR 1 of 3 in a hardening series. Merge order: this PR → "SSRF guard + approval tokens" → "resource limits + model allowlist". The later PRs are stacked on this branch, so their diffs will show earlier commits until this one merges (use regular merge, not squash, so the follow-up diffs collapse cleanly).

## Summary The Synapse backend and memory service bound `0.0.0.0` with wildcard CORS and no auth, exposing the full unauthenticated admin/data API to the LAN. This PR: - Defaults the uvicorn bind to `127.0.0.1` (`NEXUS_BIND_HOST` override) in `management/ncp.py`. - Scopes CORS to known local origins instead of `*` on both the backend and the memory service. - Adds `TrustedHostMiddleware` to reject foreign `Host` headers, which defeats DNS-rebinding — something same-origin CORS cannot stop. `NEXUS_ALLOWED_HOSTS` / `NEXUS_ALLOWED_ORIGINS` allow opt-in LAN exposure, intended to be paired with real authentication. ## Testing - Verified services listen only on `127.0.0.1` after the change. - Probed endpoints with foreign `Origin` and `Host` headers: foreign hosts get 400, CORS preflight only allows the local-origin allowlist. - `pytest` smoke tests pass. ## Stack note This is **PR 1 of 3** in a hardening series. Merge order: this PR → "SSRF guard + approval tokens" → "resource limits + model allowlist". The later PRs are stacked on this branch, so their diffs will show earlier commits until this one merges (use regular merge, not squash, so the follow-up diffs collapse cleanly).

Athena added 1 commit 2026-08-07 14:50:11 +00:00

feat(security): bind services to loopback with Host + CORS allowlists fe12eb1821

The Synapse backend and memory service bound 0.0.0.0 with wildcard CORS and no
auth, exposing the full unauthenticated admin/data API to the LAN. Default the
uvicorn bind to 127.0.0.1 (NEXUS_BIND_HOST override), scope CORS to known local
origins instead of "*", and add TrustedHostMiddleware to reject foreign Host
headers (which defeats DNS-rebinding, something same-origin CORS cannot stop).

NEXUS_ALLOWED_HOSTS / NEXUS_ALLOWED_ORIGINS allow opt-in LAN exposure, intended
to be paired with real authentication.

Co-authored-by: Cursor <cursoragent@cursor.com>

enderofwings marked the pull request as work in progress 2026-08-07 15:36:13 +00:00

enderofwings closed this pull request

2026-08-07 15:52:43 +00:00

enderofwings marked the pull request as ready for review 2026-08-07 15:59:54 +00:00

Pull request closed

Please reopen this pull request to perform a merge.

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Reference: enderofwings/NexusOS#1

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