diff --git a/lib/child_process.js b/lib/child_process.js
index 824af65556e32b..0e3e04af0d6e32 100644
--- a/lib/child_process.js
+++ b/lib/child_process.js
@@ -547,10 +547,26 @@ function getPermissionModelFlagsToCopy() {
   return permissionModelFlagsToCopy;
 }
 
+function hasPermissionFlagInEnv(nodeOptions) {
+  // Parse NODE_OPTIONS into individual tokens and check if any token
+  // is an actual --permission or --permission-audit flag. We use exact
+  // token matching rather than substring matching to avoid false positives
+  // when unrelated option values contain '--permission' (e.g.,
+  // --title=--permission).
+  if (!nodeOptions) return false;
+  const tokens = nodeOptions.split(/\s+/);
+  return tokens.some((token) =>
+    token === '--permission' ||
+    token.startsWith('--permission=') ||
+    token === '--permission-audit' ||
+    token.startsWith('--permission-audit='),
+  );
+}
+
 function copyPermissionModelFlagsToEnv(env, key, args) {
   // Do not override if permission was already passed to file
   if (args.includes('--permission') || args.includes('--permission-audit') ||
-      (env[key] && env[key].indexOf('--permission') !== -1)) {
+      hasPermissionFlagInEnv(env[key])) {
     return;
   }
 
diff --git a/test/parallel/test-permission-child-process-inherit-flags-substring.js b/test/parallel/test-permission-child-process-inherit-flags-substring.js
new file mode 100644
index 00000000000000..f992a1f3dc8f3b
--- /dev/null
+++ b/test/parallel/test-permission-child-process-inherit-flags-substring.js
@@ -0,0 +1,96 @@
+// Flags: --permission --allow-child-process --allow-fs-read=* --allow-worker
+// Tests that NODE_OPTIONS values containing '--permission' as a substring
+// in unrelated option values (e.g., --title=--permission) do NOT suppress
+// Permission Model flag propagation to child processes.
+'use strict';
+
+const common = require('../common');
+const { isMainThread } = require('worker_threads');
+
+if (!isMainThread) {
+  common.skip('This test only works on a main thread');
+}
+if (process.config.variables.node_without_node_options) {
+  common.skip('missing NODE_OPTIONS support');
+}
+
+const assert = require('assert');
+const childProcess = require('child_process');
+
+// Verify that the parent has Permission Model enabled
+assert.ok(process.permission.has('child'));
+assert.strictEqual(process.env.NODE_OPTIONS, undefined);
+
+// Test cases: NODE_OPTIONS values that contain '--permission' as a substring
+// but are NOT actual permission flags. These should NOT suppress propagation.
+const testCases = [
+  { name: 'title', nodeOptions: '--title=--permission' },
+  { name: 'conditions', nodeOptions: '--conditions=--permission' },
+  { name: 'trace-event-categories', nodeOptions: '--trace-event-categories=--permission' },
+  { name: 'title-audit', nodeOptions: '--title=--permission-audit' },
+];
+
+for (const { name, nodeOptions } of testCases) {
+  // Spawn a child with the problematic NODE_OPTIONS value.
+  // Without the fix, the substring check causes propagation to be skipped,
+  // and the child will not have process.permission.
+  const { status, stdout } = childProcess.spawnSync(
+    process.execPath,
+    [
+      '-e',
+      `
+      console.log(typeof process.permission);
+      console.log(process.permission && process.permission.has("child"));
+      console.log(process.env.NODE_OPTIONS);
+      `,
+    ],
+    {
+      env: {
+        ...process.env,
+        'NODE_OPTIONS': nodeOptions,
+      }
+    }
+  );
+
+  assert.strictEqual(status, 0, `child process for ${name} exited with status ${status}`);
+
+  const [permType, hasChild] = stdout.toString().split('\n');
+
+  // Verify the child has Permission Model enabled (the bug caused it to be absent)
+  assert.strictEqual(permType, 'object', `child ${name} should have process.permission object`);
+
+  // Verify the child inherited child permission
+  assert.strictEqual(hasChild, 'true', `child ${name} should have child permission`);
+}
+
+// Also verify that a child with a real --permission flag in NODE_OPTIONS
+// still gets its own flags honored (regression test for existing behavior).
+{
+  const { status, stdout } = childProcess.spawnSync(
+    process.execPath,
+    [
+      '-e',
+      `
+      console.log(process.permission.has("fs.write"));
+      console.log(process.permission.has("fs.read"));
+      console.log(process.permission.has("child"));
+      `,
+    ],
+    {
+      env: {
+        ...process.env,
+        'NODE_OPTIONS': '--permission --allow-fs-write=*',
+      }
+    }
+  );
+
+  assert.strictEqual(status, 0);
+  const [fsWrite, fsRead, child] = stdout.toString().split('\n');
+  assert.strictEqual(fsWrite, 'true');
+  assert.strictEqual(fsRead, 'false');
+  assert.strictEqual(child, 'false');
+}
+
+{
+  assert.strictEqual(process.env.NODE_OPTIONS, undefined);
+}