diff --git a/package.json b/package.json
index 743134cea027a..1380678cc5d74 100644
--- a/package.json
+++ b/package.json
@@ -168,6 +168,7 @@
     "auto-release-sinon": "1.0.3",
     "babel-eslint": "4.1.8",
     "chai": "3.5.0",
+    "cheerio": "0.22.0",
     "chokidar": "1.6.0",
     "chromedriver": "2.24.1",
     "elasticdump": "2.1.1",
diff --git a/src/server/status/states.js b/src/server/status/states.js
index 8c6f3fb90b09d..433faaf3c4728 100644
--- a/src/server/status/states.js
+++ b/src/server/status/states.js
@@ -45,7 +45,7 @@ exports.all = [
     severity: -1,
     icon: 'toggle-off',
     nicknames: [
-      'I\'m I even a thing?'
+      'Am I even a thing?'
     ]
   }
 ];
diff --git a/src/ui/__tests__/fixtures/test_app/index.js b/src/ui/__tests__/fixtures/test_app/index.js
new file mode 100644
index 0000000000000..4f5115faff151
--- /dev/null
+++ b/src/ui/__tests__/fixtures/test_app/index.js
@@ -0,0 +1,13 @@
+module.exports = kibana => new kibana.Plugin({
+  uiExports: {
+    app: {
+      name: 'test_app',
+      main: 'plugins/test_app/index.js',
+      injectVars() {
+        return {
+          from_test_app: true
+        };
+      }
+    }
+  }
+});
diff --git a/src/ui/__tests__/fixtures/test_app/package.json b/src/ui/__tests__/fixtures/test_app/package.json
new file mode 100644
index 0000000000000..3aeb029e4f4cc
--- /dev/null
+++ b/src/ui/__tests__/fixtures/test_app/package.json
@@ -0,0 +1,4 @@
+{
+  "name": "test_app",
+  "version": "kibana"
+}
diff --git a/src/ui/__tests__/fixtures/test_app/public/index.js b/src/ui/__tests__/fixtures/test_app/public/index.js
new file mode 100644
index 0000000000000..e69de29bb2d1d
diff --git a/src/ui/__tests__/ui_exports_replace_injected_vars.js b/src/ui/__tests__/ui_exports_replace_injected_vars.js
new file mode 100644
index 0000000000000..fe578642eae84
--- /dev/null
+++ b/src/ui/__tests__/ui_exports_replace_injected_vars.js
@@ -0,0 +1,125 @@
+import { resolve } from 'path';
+
+import { delay } from 'bluebird';
+import expect from 'expect.js';
+import sinon from 'sinon';
+import cheerio from 'cheerio';
+import { noop } from 'lodash';
+
+import KbnServer from '../../server/kbn_server';
+
+const getInjectedVarsFromResponse = (resp) => {
+  const $ = cheerio.load(resp.payload);
+  const data = $('kbn-initial-state').attr('data');
+  return JSON.parse(data).vars;
+};
+
+const injectReplacer = (kbnServer, replacer) => {
+  // normally the replacer would be defined in a plugin's uiExports,
+  // but that requires stubbing out an entire plugin directory for
+  // each test, so we fake it and jam the replacer into uiExports
+  kbnServer.uiExports.injectedVarsReplacers.push(replacer);
+};
+
+describe('UiExports', function () {
+  describe('#replaceInjectedVars', function () {
+    this.slow(2000);
+    this.timeout(10000);
+
+    let kbnServer;
+    beforeEach(async () => {
+      kbnServer = new KbnServer({
+        server: { port: 0 }, // pick a random open port
+        logging: { silent: true }, // no logs
+        optimize: { enabled: false },
+        uiSettings: { enabled: false },
+        plugins: {
+          paths: [resolve(__dirname, './fixtures/test_app')] // inject an app so we can hit /app/{id}
+        },
+      });
+
+      await kbnServer.ready();
+      kbnServer.status.get('ui settings').state = 'green';
+      kbnServer.server.decorate('server', 'uiSettings', () => {
+        return { getDefaults: noop };
+      });
+    });
+
+    afterEach(async () => {
+      await kbnServer.close();
+      kbnServer = null;
+    });
+
+    it('allows sync replacing of injected vars', async () => {
+      injectReplacer(kbnServer, () => ({ a: 1 }));
+
+      const resp = await kbnServer.inject('/app/test_app');
+      const injectedVars = getInjectedVarsFromResponse(resp);
+
+      expect(injectedVars).to.eql({ a: 1 });
+    });
+
+    it('allows async replacing of injected vars', async () => {
+      const asyncThing = () => delay(100).return('world');
+
+      injectReplacer(kbnServer, async () => {
+        return {
+          hello: await asyncThing()
+        };
+      });
+
+      const resp = await kbnServer.inject('/app/test_app');
+      const injectedVars = getInjectedVarsFromResponse(resp);
+
+      expect(injectedVars).to.eql({
+        hello: 'world'
+      });
+    });
+
+    it('passes originalInjectedVars, request, and server to replacer', async () => {
+      const stub = sinon.stub();
+      injectReplacer(kbnServer, () => ({ foo: 'bar' }));
+      injectReplacer(kbnServer, stub);
+
+      await kbnServer.inject('/app/test_app');
+
+      sinon.assert.calledOnce(stub);
+      expect(stub.firstCall.args[0]).to.eql({ foo: 'bar' }); // originalInjectedVars
+      expect(stub.firstCall.args[1]).to.have.property('path', '/app/test_app'); // request
+      expect(stub.firstCall.args[1]).to.have.property('server', kbnServer.server); // request
+      expect(stub.firstCall.args[2]).to.be(kbnServer.server);
+    });
+
+    it('calls the methods sequentially', async () => {
+      injectReplacer(kbnServer, () => ({ name: '' }));
+      injectReplacer(kbnServer, orig => ({ name: orig.name + 's' }));
+      injectReplacer(kbnServer, orig => ({ name: orig.name + 'a' }));
+      injectReplacer(kbnServer, orig => ({ name: orig.name + 'm' }));
+
+      const resp = await kbnServer.inject('/app/test_app');
+      const injectedVars = getInjectedVarsFromResponse(resp);
+
+      expect(injectedVars).to.eql({ name: 'sam' });
+    });
+
+    it('propogates errors thrown in replacers', async () => {
+      injectReplacer(kbnServer, async () => {
+        await delay(100);
+        throw new Error('replacer failed');
+      });
+
+      const resp = await kbnServer.inject('/app/test_app');
+      expect(resp).to.have.property('statusCode', 500);
+    });
+
+    it('starts off with the injected vars for the app merged with the default injected vars', async () => {
+      const stub = sinon.stub();
+      injectReplacer(kbnServer, stub);
+      kbnServer.uiExports.defaultInjectedVars.from_defaults = true;
+
+      const resp = await kbnServer.inject('/app/test_app');
+      sinon.assert.calledOnce(stub);
+      expect(stub.firstCall.args[0]).to.eql({ from_defaults: true, from_test_app: true });
+    });
+  });
+});
diff --git a/src/ui/index.js b/src/ui/index.js
index 1325681343c52..c88ec53c82e6f 100644
--- a/src/ui/index.js
+++ b/src/ui/index.js
@@ -2,6 +2,7 @@ import { format as formatUrl } from 'url';
 import { readFileSync as readFile } from 'fs';
 import { defaults } from 'lodash';
 import Boom from 'boom';
+import { reduce as reduceAsync } from 'bluebird';
 import { resolve } from 'path';
 import fromRoot from '../utils/from_root';
 import UiExports from './ui_exports';
@@ -43,15 +44,19 @@ export default async (kbnServer, server, config) => {
   server.route({
     path: '/app/{id}',
     method: 'GET',
-    handler: function (req, reply) {
+    async handler(req, reply) {
       const id = req.params.id;
       const app = uiExports.apps.byId[id];
       if (!app) return reply(Boom.notFound('Unknown app ' + id));
 
-      if (kbnServer.status.isGreen()) {
-        return reply.renderApp(app);
-      } else {
-        return reply.renderStatusPage();
+      try {
+        if (kbnServer.status.isGreen()) {
+          await reply.renderApp(app);
+        } else {
+          await reply.renderStatusPage();
+        }
+      } catch (err) {
+        reply(Boom.wrap(err));
       }
     }
   });
@@ -70,7 +75,11 @@ export default async (kbnServer, server, config) => {
         defaults: await server.uiSettings().getDefaults(),
         user: {}
       },
-      vars: defaults(app.getInjectedVars() || {}, uiExports.defaultInjectedVars),
+      vars: await reduceAsync(
+        uiExports.injectedVarsReplacers,
+        async (acc, replacer) => await replacer(acc, this.request, server),
+        defaults(await app.getInjectedVars() || {}, uiExports.defaultInjectedVars)
+      )
     };
   }
 
@@ -83,16 +92,18 @@ export default async (kbnServer, server, config) => {
   }
 
   async function renderApp(app) {
-    const isElasticsearchPluginRed = server.plugins.elasticsearch.status.state === 'red';
-    const payload = await getPayload(app);
-    if (!isElasticsearchPluginRed) {
+    const payload = await getPayload.call(this, app);
+
+    const esStatus = kbnServer.status.getForPluginId('elasticsearch');
+    if (esStatus && esStatus.state !== 'red') {
       payload.uiSettings.user = await server.uiSettings().getUserProvided();
     }
+
     return viewAppWithPayload.call(this, app, payload);
   }
 
   async function renderAppWithDefaultConfig(app) {
-    const payload = await getPayload(app);
+    const payload = await getPayload.call(this, app);
     return viewAppWithPayload.call(this, app, payload);
   }
 
diff --git a/src/ui/ui_exports.js b/src/ui/ui_exports.js
index 2bb3ccfac681c..2e84ca8340397 100644
--- a/src/ui/ui_exports.js
+++ b/src/ui/ui_exports.js
@@ -14,6 +14,7 @@ class UiExports {
     this.consumers = [];
     this.bundleProviders = [];
     this.defaultInjectedVars = {};
+    this.injectedVarsReplacers = [];
   }
 
   consumePlugin(plugin) {
@@ -107,6 +108,11 @@ class UiExports {
             _.merge(this.defaultInjectedVars, await injector.call(plugin, server, options));
           });
         };
+
+      case 'replaceInjectedVars':
+        return (plugin, replacer) => {
+          this.injectedVarsReplacers.push(replacer);
+        };
     }
   }