diff --git a/docs/security/BITCOIN-RPC-PROXY-EXPOSURE.md b/docs/security/BITCOIN-RPC-PROXY-EXPOSURE.md
new file mode 100644
index 00000000..b605b528
--- /dev/null
+++ b/docs/security/BITCOIN-RPC-PROXY-EXPOSURE.md
@@ -0,0 +1,89 @@
+# The Bitcoin RPC proxy that stayed open after it was fixed
+
+**Status:** code fix committed (`f6b5245b`); on-node verification recorded below.
+**Found:** 2026-08-02, archi-dev-box, while verifying `a05956c4` instead of assuming it.
+**Severity:** critical on any affected node — unauthenticated control of Bitcoin Core RPC
+through a proxy that injects the node's own credentials.
+
+## Why this document exists
+
+`a05956c4` closed two unauthenticated endpoints on the wallet UI ports. Its commit message
+stated:
+
+> The nginx template is `include_str!`'d and re-rendered on every reconcile pass, so this
+> ships atomically with the binary.
+
+That is true for most nodes and false for a specific, silent, and not-rare state. The half
+that landed correctly (LND) made the half that did not (Bitcoin RPC) *harder* to notice,
+because a spot check of the LND endpoint returns a clean `401` and reads as "patched".
+
+## What was observed
+
+Node running the fixed binary (installed 17:21, contains the new template — `auth_request`
+present in the binary at 4 occurrences). All probes from the node's own LAN address, no
+cookies, no credentials:
+
+| Probe | Result |
+|---|---|
+| `GET http://192.168.63.240:18083/lnd-connect-info` | `401`, 24 bytes, `{"error":"Unauthorized"}` — **closed** |
+| `POST http://192.168.63.240:8334/bitcoin-rpc/` (`getblockcount`) | `200` — `{"result":960774,"error":null}` — **OPEN** |
+| `OPTIONS http://192.168.63.240:8334/bitcoin-rpc/` | `204` with `Access-Control-Allow-Origin: *` — **OPEN** |
+
+The rendered config on disk, `/var/lib/archipelago/bitcoin-ui/nginx.conf`, was dated
+**2026-06-30** — the pre-fix version, with no `auth_request` and with the wildcard CORS
+header the fix removes.
+
+## Root cause
+
+Three facts have to be true at once, and on this node they were:
+
+1. `bitcoin-ui` is listed in the node's durable `user-uninstalled` marker
+   (`/var/lib/archipelago/user-uninstalled.json`).
+2. `reconcile_app` returns on that marker (`prod_orchestrator.rs:1956`) **before** reaching
+   `run_pre_start_hooks`, which is the only thing that renders the nginx config.
+3. The container keeps running anyway, because it is owned by **systemd via a Quadlet
+   unit** — `archy-bitcoin-ui.service`, `active`, restarted 17:25 after the daemon restart —
+   not by the reconciler that is refusing to touch it.
+
+So: *a container systemd keeps alive, that the orchestrator has stopped reconciling, never
+receives a config fix shipped inside the binary.* The marker means "must stay removed", but
+nothing enforces removal against systemd, and the orchestrator treats the marker as
+permission to stop looking.
+
+This is not a one-app accident. On the same node `archy-electrs-ui` is in the identical
+state (uninstalled marker + active Quadlet unit + `Up 10 days`). It serves only a static
+page with no credential-injecting proxy, so its exposure is low — but it would miss any
+future config fix the same way.
+
+## Why it matters beyond this node
+
+An OTA carrying `a05956c4` would have closed the LND leak everywhere and silently failed to
+close the Bitcoin RPC proxy on every node in this state — while making those nodes *look*
+patched to exactly the check an operator would run first. That is the most misleading
+possible outcome of shipping a security fix.
+
+## The fix
+
+`f6b5245b`: a container that is actually running is a live attack surface whatever a marker
+says about it, so its security-relevant config is reconciled even behind the marker, and the
+container is restarted so nginx loads it.
+
+Deliberately narrow:
+
+- Nothing is created, pulled, built, started or resurrected. The "must stay removed"
+  contract can only weaken for a container that is **already running**, which by definition
+  means it was never removed.
+- A hook error is swallowed, not propagated — an app the user uninstalled must not be able
+  to fail the reconcile pass for every app after it.
+- The pre-existing marker test passes unchanged; that is what proves the removal contract
+  survived. A new regression test pins the whole chain: stale conf in, gate present out,
+  container restarted, nothing created.
+
+## Operator note
+
+Deploying the fix rewrites the config and restarts `archy-bitcoin-ui` (a brief Bitcoin UI
+interruption, nothing else). Any node that ever had `bitcoin-ui` uninstalled while its
+Quadlet unit stayed active should be re-probed with the `POST /bitcoin-rpc/` check above —
+a `401` is the pass condition. Treat the Bitcoin RPC password on any node that answered
+`200` as known to anyone who could reach that port, and rotate it **after** the fix is
+deployed, never before.