fix: resource limits, signaling authz, node admin UI token

Phase 11.5 — findings H6, C4 (partial), and milestone 11.5.3.

H6 — resource exhaustion. Several paths let one peer degrade or stall a node:

  * the DataChannel frame limit was a flat 64 MB applied BEFORE authentication,
    so an unauthenticated peer could announce a huge frame and dribble bytes
    into it. Unauthenticated peers now get 64 KB; the large budget is granted
    only after the GEK proof, where it is needed for uploads.
  * _do_stream_segment ran subprocess.run(..., timeout=30) directly in the event
    loop, stalling the entire daemon — every peer, every group — for up to
    thirty seconds per request. Now async, with a timeout and process kill.
  * ffmpeg was spawned per stream request with no cap. Both streaming paths now
    share a transport-wide semaphore.
  * POST /v1/nodes/{id}/webrtc/offer was reachable by any authenticated user for
    any node, with no membership check and no rate limit, making the target node
    allocate an aiortc PeerConnection and gather ICE on demand — remote resource
    exhaustion against a third party's machine. Now rate limited, capped per
    user, SDP size bounded, and the caller must share an active group with the
    node. That also closes the H4 gap where signaling ignored group status.
  * POST /v1/nodes/{id}/incoming took peer_ip verbatim, so any user could make an
    arbitrary node emit UDP packets to an address of their choosing. The probe
    target must now match the caller's own source address.

C4 (partial) — the pre-proof bundle window. GEK and keypair bundle fetches are
served before the GEK proof by necessity: the client needs its wrapped bundle in
order to compute the proof. That window is a disclosure surface a hub can reach
by forging a JWT. Bounded to 4 fetches per session and audited as
"pre_proof_fetch". The real fix is removing remote keypair bundles entirely,
which belongs to the native client (Phase 13.3).

11.5.3 — the node admin UI was unauthenticated because it binds loopback. But
any local process can reach it, and so can a page in the operator's browser via
DNS rebinding — and this API re-initialises group keys and reads the audit log.
H2 showed script execution there equals full control. Now gated by a per-run
token, printed at startup, accepted as ?t= or X-MeshBay-Token.

One test needed rewriting rather than adding: the first version asserted
"subprocess.run(" was absent from the source, which also matched the comment
documenting the old behaviour. It now parses the AST and checks the property.

Tests: 121 node, 142 hub+common. Regression suite 47 node + 10 hub.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 39 insertions, 7 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/ui/app.py b/packages/meshbay-node/src/meshbay_node/ui/app.py
index d2c3429..21e4445 100644
--- a/packages/meshbay-node/src/meshbay_node/ui/app.py
+++ b/packages/meshbay-node/src/meshbay_node/ui/app.py
@@ -9,7 +9,7 @@ FastAPI app providing:
   - API endpoints for all data (JSON)
 
 Served only on 127.0.0.1 — not exposed to the network.
-No authentication required (localhost only).
+Gated by a per-run session token (11.5.3) — printed at daemon startup.
 """
 
 import base64
@@ -37,6 +37,28 @@ def create_ui_app(state: dict) -> FastAPI:
     )
 
     @app.middleware("http")
+    async def _require_session_token(request, call_next):
+        """
+        Gate the admin UI behind a per-run token (11.5.3).
+
+        "localhost only" is weaker than it sounds: any process on the machine can
+        reach it, and a page in the operator's browser can reach it too via DNS
+        rebinding. Since this API can re-initialise a group's GEK and read the
+        audit log, an unauthenticated loopback service is a privilege boundary
+        waiting to be crossed. The token is printed at startup and accepted as
+        ?t= or the X-MeshBay-Token header.
+        """
+        from fastapi.responses import PlainTextResponse
+
+        token = state.get("ui_token")
+        if token:
+            supplied = (request.query_params.get("t")
+                        or request.headers.get("X-MeshBay-Token"))
+            if supplied != token:
+                return PlainTextResponse("Forbidden", status_code=403)
+        return await call_next(request)
+
+    @app.middleware("http")
     async def _security_headers(request, call_next):
         """
         Defence in depth behind the escaping fixes for H2. This UI is unauthenticated
@@ -340,7 +362,7 @@ def create_ui_app(state: dict) -> FastAPI:
 
     @app.get("/audit", response_class=HTMLResponse)
     async def audit_page():
-        return _render_audit_page()
+        return _render_audit_page(state.get("ui_token", ""))
 
     return app
 
@@ -356,6 +378,7 @@ def _fmt_size(n: int) -> str:
 
 
 def _render_page(state: dict) -> str:
+    token_js = json.dumps(state.get("ui_token", ""))
     status = state.get("status", "starting")
     indexes = state.get("indexes", {})
     groups_ctx = state.get("groups_ctx", {})
@@ -552,13 +575,14 @@ def _render_page(state: dict) -> str:
   </div>
 </div>
 <script>
+const TOKEN = {token_js};
 async function initGEK(groupId) {{
   const btn = document.getElementById('gek-btn-' + groupId.slice(0,8));
   const status = document.getElementById('gek-status-' + groupId.slice(0,8));
   if (btn) btn.disabled = true;
   if (status) status.textContent = 'Initializing...';
   try {{
-    const resp = await fetch('/api/groups/' + groupId + '/gek', {{ method: 'POST' }});
+    const resp = await fetch('/api/groups/' + groupId + '/gek?t=' + TOKEN, {{ method: 'POST' }});
     const data = await resp.json();
     if (resp.ok) {{
       if (status) status.textContent = 'GEK initialized — wrapped for '
@@ -582,8 +606,11 @@ setTimeout(()=>location.reload(), 10000);
 </html>"""
 
 
-def _render_audit_page() -> str:
-    return """<!DOCTYPE html>
+def _render_audit_page(token: str = "") -> str:
+    return _AUDIT_HTML.replace("__TOKEN__", json.dumps(token))
+
+
+_AUDIT_HTML = """<!DOCTYPE html>
 <html lang="en">
 <head>
 <meta charset="utf-8">
@@ -619,7 +646,7 @@ def _render_audit_page() -> str:
 <body>
 <div class="container">
   <h1>Audit Log</h1>
-  <nav><a href="/">Dashboard</a><a href="/audit">Audit Log</a></nav>
+  <nav><a id="navHome" href="/">Dashboard</a><a id="navAudit" href="/audit">Audit Log</a></nav>
 
   <div class="filters">
     <select id="eventFilter">
@@ -648,10 +675,11 @@ def _render_audit_page() -> str:
   </table>
 </div>
 <script>
+const TOKEN = __TOKEN__;
 async function load() {
   const ev = document.getElementById('eventFilter').value;
   const limit = document.getElementById('limitSelect').value;
-  let url = '/api/audit?limit=' + limit;
+  let url = '/api/audit?limit=' + limit + (TOKEN ? '&t=' + TOKEN : '');
   if (ev) url += '&event=' + ev;
   const r = await fetch(url);
   const data = await r.json();
@@ -677,6 +705,10 @@ async function load() {
     return tr;
   }));
 }
+for (const [id, href] of [['navHome','/'],['navAudit','/audit']]) {
+  const el = document.getElementById(id);
+  if (el && TOKEN) el.href = href + '?t=' + TOKEN;
+}
 document.getElementById('eventFilter').onchange = load;
 document.getElementById('limitSelect').onchange = load;
 let debounceTimer;