diff --git a/server/express.js b/server/express.js
index 4c65a57b061..d7d30bbd118 100644
--- a/server/express.js
+++ b/server/express.js
@@ -709,6 +709,13 @@ function makeApp(authAddress, cdapConfig, uiSettings) {
    * be used and we need to persist this information somewhere.
    */
   app.post('/updateTheme', function (req, res) {
+    // This endpoint is only for testing themes in development and must not be
+    // active in production (it has no persistent effect and opens unnecessary
+    // attack surface). Return 401 so callers get a clear signal rather than a
+    // silent no-op.
+    if (isModeProduction()) {
+      return res.status(401).send('This endpoint is not available in production');
+    }
     let authToken = req.headers.authorization;
     if (
       !req.headers['session-token'] ||
@@ -717,10 +724,24 @@ function makeApp(authAddress, cdapConfig, uiSettings) {
     ) {
       return res.status(500).send('Unable to validate session');
     }
-    const uiThemePath = req.body.uiThemePath;
-    if (!uiThemePath) {
+    const requestedTheme = req.body.uiThemePath;
+    if (typeof requestedTheme !== 'string' || !requestedTheme) {
+      return res.status(500).send('UnKnown theme file. Please make sure the path is valid');
+    }
+    // This endpoint exists to switch between the theme files shipped in
+    // config/themes/ for testing (see doc comment above), not to load an
+    // arbitrary path. Resolve to a filename within that directory only,
+    // discarding any directory component the client supplies, so this can't
+    // be used to point at a file elsewhere on the filesystem. path.basename
+    // returns '..' or '.' unchanged for those exact inputs (it only strips
+    // directory components, it doesn't resolve '..' segments), so those two
+    // values need an explicit reject or they'd resolve one level above
+    // config/themes/.
+    const baseTheme = path.basename(requestedTheme);
+    if (baseTheme === '..' || baseTheme === '.' || !baseTheme) {
       return res.status(500).send('UnKnown theme file. Please make sure the path is valid');
     }
+    const uiThemePath = path.join(__dirname, 'config', 'themes', baseTheme);
     try {
       uiThemeConfig = uiThemeWrapper.extractUITheme(cdapConfig, uiThemePath);
     } catch (e) {
diff --git a/server/token.mjs b/server/token.mjs
index 2c06a1ebb94..862d563b446 100644
--- a/server/token.mjs
+++ b/server/token.mjs
@@ -15,8 +15,11 @@
 */
 
 import crypto from 'crypto';
+import fs from 'fs';
 import path from 'path';
 
+/* global process, __dirname */
+
 const EncryptionConstants = {
   ONE_HOUR_MILLIS: 60 * 60 * 1000,
   /**
@@ -97,15 +100,23 @@ function decrypt(encText, key) {
 }
 
 function getSecretFromCDAPConfig(cdapConfig, logger) {
-  let secretKey =
-    cdapConfig['session.secret.key'] ||
-    path.resolve(__dirname, 'config', 'development', 'session.secret.key');
   if (!logger) {
     logger = console;
   }
+  const secretKey = cdapConfig['session.secret.key'];
   if (!secretKey) {
-    logger.warn(
-      'Secret key missing. This is required to generate a strong time-based token to prevent cswh'
+    // In development, fall back to reading the actual secret file on disk.
+    // This avoids the old bug where the file *path string* was used as key
+    // material instead of the file's contents.
+    if (process.env.NODE_ENV === 'development') {
+      const keyFilePath = path.resolve(__dirname, 'config', 'development', 'session_secret.key');
+      return fs.readFileSync(keyFilePath, 'utf8');
+    }
+    // In production (or any other environment), fail closed: a deployment
+    // must explicitly configure a real secret via 'session.secret.key'.
+    throw new Error(
+      "'session.secret.key' is not configured. A real secret is required to generate " +
+        'or validate session tokens.'
     );
   }
   return secretKey;
diff --git a/server/token_test.mjs b/server/token_test.mjs
index d492226eb26..65a9606ae3c 100644
--- a/server/token_test.mjs
+++ b/server/token_test.mjs
@@ -41,5 +41,30 @@ function testMismatch() {
   assert(!isTokenValid);
 }
 
+// A missing 'session.secret.key' must not fall back to any predictable value.
+// generateToken should refuse to issue a token, and validateToken should
+// reject everything (including a token forged with the old, predictable
+// fallback), rather than accepting a guessable secret.
+function testMissingSecretKeyRefusesToken() {
+  const cdapConfigNoSecret = { 'instance.metadata.id': 'test-instance' };
+
+  let threw = false;
+  try {
+    generateToken(cdapConfigNoSecret, console);
+  } catch (e) {
+    threw = true;
+  }
+  assert(threw, 'generateToken should throw when session.secret.key is not configured');
+
+  const isValid = validateToken('anything-at-all', cdapConfigNoSecret, console);
+  assert(!isValid, 'validateToken should reject when session.secret.key is not configured');
+
+  console.log('testMissingSecretKeyRefusesToken passed');
+}
+
 testMatch();
+testMissingSecretKeyRefusesToken();
+// Note: testMismatch() fails on master independent of this change, since
+// authToken isn't actually part of the token or the comparison in either
+// generateToken or validateToken. Left as-is, out of scope here.
 testMismatch();
diff --git a/server/uiThemeWrapper.js b/server/uiThemeWrapper.js
index b53464bcbe0..2eae1f77f86 100644
--- a/server/uiThemeWrapper.js
+++ b/server/uiThemeWrapper.js
@@ -50,6 +50,12 @@ function extractUIFeaturesFromConfig(cdapConfig) {
   return featuresMap;
 }
 
+// Theme files are plain JSON data, not code. Read and parse them directly
+// instead of require()'ing them to avoid executing attacker-controlled input.
+function readThemeJSON(themePath) {
+  return JSON.parse(fs.readFileSync(themePath, 'utf8'));
+}
+
 function mergeUIThemeWithConfig(cdapConfig, themeConfig) {
   const configFeatures = {
     features: extractUIFeaturesFromConfig(cdapConfig),
@@ -71,11 +77,9 @@ export function extractUITheme(cdapConfig, uiThemePath) {
   // Absolute path
   if (uiThemePath[0] === '/') {
     try {
-      if (__non_webpack_require__.resolve(uiThemePath)) {
-        uiThemeConfig = __non_webpack_require__(uiThemePath);
-        log.info(`UI using theme file: ${uiThemePath}`);
-        return mergeUIThemeWithConfig(cdapConfig, uiThemeConfig);
-      }
+      uiThemeConfig = readThemeJSON(uiThemePath);
+      log.info(`UI using theme file: ${uiThemePath}`);
+      return mergeUIThemeWithConfig(cdapConfig, uiThemeConfig);
     } catch (e) {
       log.info('UI Theme file not found at: ', uiThemePath);
       throw e;
@@ -105,11 +109,9 @@ export function extractUITheme(cdapConfig, uiThemePath) {
       }
       themePath = path.join(__dirname, themePath);
 
-      if (__non_webpack_require__.resolve(themePath)) {
-        uiThemeConfig = __non_webpack_require__(themePath);
-        log.info(`UI using theme file: ${themePath}`);
-        return mergeUIThemeWithConfig(cdapConfig, uiThemeConfig);
-      }
+      uiThemeConfig = readThemeJSON(themePath);
+      log.info(`UI using theme file: ${themePath}`);
+      return mergeUIThemeWithConfig(cdapConfig, uiThemeConfig);
     } catch (e) {
       // This will show the user what the full path is.
       // This should help them give proper relative path
diff --git a/server/uiThemeWrapper.test.js b/server/uiThemeWrapper.test.js
new file mode 100644
index 00000000000..7b7e43314fc
--- /dev/null
+++ b/server/uiThemeWrapper.test.js
@@ -0,0 +1,51 @@
+/*
+ * Copyright © 2026 Cask Data, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+import fs from 'fs';
+import os from 'os';
+import path from 'path';
+import { extractUITheme } from 'server/uiThemeWrapper';
+
+describe('extractUITheme', () => {
+  const cdapConfig = { 'ui.theme.file': true };
+
+  test('loads a plain JSON theme file', () => {
+    const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'ui-theme-test-'));
+    const themePath = path.join(dir, 'theme.json');
+    fs.writeFileSync(themePath, JSON.stringify({ content: { theme: 'ok' } }));
+
+    const result = extractUITheme(cdapConfig, themePath);
+    expect(result.content.theme).toBe('ok');
+  });
+
+  // Regression test: extractUITheme used to load the theme file with
+  // __non_webpack_require__, which executes .js files as Node modules
+  // instead of just reading them as data. A path ending in .js that runs
+  // code (instead of failing to parse as JSON) means this is still
+  // executing the file rather than reading it.
+  test('does not execute a .js file passed as the theme path', () => {
+    const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'ui-theme-test-'));
+    const canaryPath = path.join(dir, 'canary.txt');
+    const themePath = path.join(dir, 'theme.js');
+    fs.writeFileSync(
+      themePath,
+      `require('fs').writeFileSync(${JSON.stringify(canaryPath)}, 'executed');\nmodule.exports = { content: { theme: 'pwned' } };\n`
+    );
+
+    expect(() => extractUITheme(cdapConfig, themePath)).toThrow();
+    expect(fs.existsSync(canaryPath)).toBe(false);
+  });
+});