diff --git a/packages/cli/test/integration/task-runners/js-task-runner-execution.integration.test.ts b/packages/cli/test/integration/task-runners/js-task-runner-execution.integration.test.ts
index bb0dd4dfb53..6bbe5be746d 100644
--- a/packages/cli/test/integration/task-runners/js-task-runner-execution.integration.test.ts
+++ b/packages/cli/test/integration/task-runners/js-task-runner-execution.integration.test.ts
@@ -212,6 +212,27 @@ describe('JS TaskRunner execution on internal mode', () => {
 				result: { hello: 'world' },
 			});
 		});
+
+		// CAT-3208 / GH #24307: secure-mode task runners disable code generation
+		// (--disallow-code-generation-from-strings) and freeze Object.prototype, so
+		// expressions can't be evaluated inside the Code node. $evaluateExpression
+		// must surface a clear, actionable error instead of crashing with
+		// "Cannot assign to read only property '__lookupGetter__'" or silently
+		// returning null.
+		it('should throw a clear error for $evaluateExpression in the Code node', async () => {
+			// Act
+			const result = await runTaskWithCode("return { val: $evaluateExpression('{{ 1 + 1 }}') }");
+
+			// Assert
+			expect(result).toEqual({
+				ok: false,
+				error: expect.objectContaining({
+					message: expect.stringContaining(
+						'in the Code node while task runners run in secure mode',
+					),
+				}),
+			});
+		});
 	});
 
 	describe('Internal and external libs', () => {
diff --git a/packages/workflow/src/expression.ts b/packages/workflow/src/expression.ts
index d0a8bcec0ed..77b9a948b66 100644
--- a/packages/workflow/src/expression.ts
+++ b/packages/workflow/src/expression.ts
@@ -373,10 +373,23 @@ export class Expression {
 		data.Reflect = {};
 		data.Proxy = {};
 
-		data.__lookupGetter__ = undefined;
-		data.__lookupSetter__ = undefined;
-		data.__defineGetter__ = undefined;
-		data.__defineSetter__ = undefined;
+		// These four names are inherited from `Object.prototype`. In the secure-mode
+		// task-runner sandbox `Object.prototype` is frozen, so plain assignment walks
+		// the prototype chain to the now read-only inherited property and throws in
+		// strict mode. Define them as own properties to overwrite them safely.
+		for (const key of [
+			'__lookupGetter__',
+			'__lookupSetter__',
+			'__defineGetter__',
+			'__defineSetter__',
+		]) {
+			Object.defineProperty(data, key, {
+				value: undefined,
+				writable: true,
+				enumerable: true,
+				configurable: true,
+			});
+		}
 
 		// Deprecated
 		data.escape = {};
diff --git a/packages/workflow/src/workflow-data-proxy.ts b/packages/workflow/src/workflow-data-proxy.ts
index 55d428d902e..aa2721197bb 100644
--- a/packages/workflow/src/workflow-data-proxy.ts
+++ b/packages/workflow/src/workflow-data-proxy.ts
@@ -52,6 +52,26 @@ const PAIRED_ITEM_METHOD = {
 
 type PairedItemMethod = (typeof PAIRED_ITEM_METHOD)[keyof typeof PAIRED_ITEM_METHOD];
 
+/**
+ * Whether the runtime can compile expressions. The expression engine compiles
+ * expressions via `new Function`, which throws when the process is started with
+ * `--disallow-code-generation-from-strings` — as the secure-mode task runner is.
+ * This is a process-wide invariant, so we probe once and cache the result.
+ */
+let codeGenerationAllowed: boolean | undefined;
+const isCodeGenerationAllowed = (): boolean => {
+	if (codeGenerationAllowed === undefined) {
+		try {
+			// eslint-disable-next-line @typescript-eslint/no-implied-eval, no-new-func
+			new Function('return 1');
+			codeGenerationAllowed = true;
+		} catch {
+			codeGenerationAllowed = false;
+		}
+	}
+	return codeGenerationAllowed;
+};
+
 export class WorkflowDataProxy {
 	private runExecutionData: IRunExecutionData | null;
 
@@ -1496,6 +1516,15 @@ export class WorkflowDataProxy {
 				that.envProviderState ?? createEnvProviderState(),
 			),
 			$evaluateExpression: (expression: string, itemIndex?: number) => {
+				if (!isCodeGenerationAllowed()) {
+					throw new ExpressionError(
+						"$evaluateExpression can't be used in the Code node while task runners run in secure mode",
+						{
+							description:
+								'Secure-mode task runners disable evaluating strings as code, which expressions rely on. Evaluate the expression in a node field instead, for example an Edit Fields (Set) node before the Code node.',
+						},
+					);
+				}
 				itemIndex = itemIndex || that.itemIndex;
 				return that.workflow.expression.getParameterValue(
 					`=${expression}`,