From 21764d5b90c8db06f5c52a1747e2e41f65da478b Mon Sep 17 00:00:00 2001
From: "Kai (Tam Nhu) Tran" <61256810+kaitranntt@users.noreply.github.com>
Date: Sat, 23 May 2026 21:44:19 -0400
Subject: [PATCH] fix(web): harden localhost guard against DNS rebinding
 (#1357)

* fix(web): harden localhost guard against DNS rebinding

* style: apply prettier formatting
---
 src/web-server/middleware/auth-middleware.ts  | 34 +++++++++++++--
 .../codex-profiles-endpoint.test.ts           | 42 +++++++++++++++++--
 2 files changed, 69 insertions(+), 7 deletions(-)

diff --git a/src/web-server/middleware/auth-middleware.ts b/src/web-server/middleware/auth-middleware.ts
index 204b4c97..296cb2cd 100644
--- a/src/web-server/middleware/auth-middleware.ts
+++ b/src/web-server/middleware/auth-middleware.ts
@@ -246,10 +246,36 @@ export function requireLocalAccessWhenAuthDisabled(
     return true;
   }
 
-  if (isLoopbackRemoteAddress(req.socket.remoteAddress)) {
-    return true;
+  if (!isLoopbackRemoteAddress(req.socket.remoteAddress)) {
+    res.status(403).json({ error });
+    return false;
   }
 
-  res.status(403).json({ error });
-  return false;
+  const host = parseHostHeader(getSingleHeader(req.headers.host));
+  if (!host || !isLoopbackHostname(host.hostname)) {
+    res.status(403).json({ error });
+    return false;
+  }
+
+  const originHeader = getSingleHeader(req.headers.origin);
+  if (originHeader) {
+    let origin: URL;
+    try {
+      origin = new URL(originHeader);
+    } catch {
+      res.status(403).json({ error });
+      return false;
+    }
+
+    const isSameHost = origin.host.toLowerCase() === host.host.toLowerCase();
+    const isLoopbackAlias =
+      isHttpOrigin(origin) && isLoopbackHostname(origin.hostname) && origin.port === host.port;
+
+    if (!isSameHost && !isLoopbackAlias) {
+      res.status(403).json({ error });
+      return false;
+    }
+  }
+
+  return true;
 }
diff --git a/tests/integration/web-server/codex-profiles-endpoint.test.ts b/tests/integration/web-server/codex-profiles-endpoint.test.ts
index 44b3ce05..1c3a71a0 100644
--- a/tests/integration/web-server/codex-profiles-endpoint.test.ts
+++ b/tests/integration/web-server/codex-profiles-endpoint.test.ts
@@ -206,9 +206,8 @@ describe('GET /api/codex/profiles', () => {
     // 127.0.0.1 and the test client connects to 127.0.0.1, the built-in fetch
     // will always be loopback. We test the guard directly via a separate
     // Express app that injects a non-loopback remote address.
-    const { requireLocalAccessWhenAuthDisabled } = await import(
-      '../../../src/web-server/middleware/auth-middleware'
-    );
+    const { requireLocalAccessWhenAuthDisabled } =
+      await import('../../../src/web-server/middleware/auth-middleware');
     const { isDashboardAuthEnabled } = await import('../../../src/config/config-loader-facade');
 
     if (!isDashboardAuthEnabled()) {
@@ -245,6 +244,43 @@ describe('GET /api/codex/profiles', () => {
     }
   });
 
+  it('returns 403 for loopback remote addresses when host/origin indicate non-local origin', async () => {
+    const { requireLocalAccessWhenAuthDisabled } =
+      await import('../../../src/web-server/middleware/auth-middleware');
+    const { isDashboardAuthEnabled } = await import('../../../src/config/config-loader-facade');
+
+    if (!isDashboardAuthEnabled()) {
+      let guardResult: boolean | undefined;
+
+      const testApp = express();
+      testApp.get('/test', (req, res) => {
+        Object.defineProperty(req, 'socket', {
+          value: { remoteAddress: '127.0.0.1' },
+          writable: true,
+          configurable: true,
+        });
+        req.headers.host = 'attacker.example.test';
+        req.headers.origin = 'http://attacker.example.test';
+
+        guardResult = requireLocalAccessWhenAuthDisabled(req, res, 'localhost only');
+        if (guardResult) {
+          res.json({ ok: true });
+        }
+      });
+
+      const testServer = await new Promise<http.Server>((resolve) => {
+        const s = testApp.listen(0, '127.0.0.1', () => resolve(s));
+      });
+      const testPort = (testServer.address() as { port: number }).port;
+
+      const res = await fetch(`http://127.0.0.1:${testPort}/test`);
+      await new Promise<void>((resolve) => testServer.close(() => resolve()));
+
+      expect(res.status).toBe(403);
+      expect(guardResult).toBe(false);
+    }
+  });
+
   it('response body contains no token substrings for a valid profile', async () => {
     const instancesDir = path.join(ccsDir, 'codex-instances');
     const workDir = path.join(instancesDir, 'work');