diff --git a/packages/plugins/apps/src/backend/ast-parsing/reject-node-builtin-imports.test.ts b/packages/plugins/apps/src/backend/ast-parsing/reject-node-builtin-imports.test.ts
new file mode 100644
index 000000000..bdbae89c5
--- /dev/null
+++ b/packages/plugins/apps/src/backend/ast-parsing/reject-node-builtin-imports.test.ts
@@ -0,0 +1,108 @@
+// Unless explicitly stated otherwise all files in this repository are licensed under the MIT License.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2019-Present Datadog, Inc.
+
+import { rejectNodeBuiltinImports } from '@dd/apps-plugin/backend/ast-parsing/reject-node-builtin-imports';
+import type { ImportDeclaration, Program } from 'estree';
+
+/**
+ * Helper to build a minimal ESTree Program for testing.
+ */
+function program(body: Program['body']): Program {
+    return { type: 'Program', sourceType: 'module', body };
+}
+
+/**
+ * Helper to build a minimal ImportDeclaration node for a given source.
+ */
+function importDecl(source: string, overrides: Partial<ImportDeclaration> = {}): ImportDeclaration {
+    return {
+        type: 'ImportDeclaration',
+        specifiers: [
+            {
+                type: 'ImportDefaultSpecifier',
+                local: { type: 'Identifier', name: 'x' },
+            },
+        ],
+        source: { type: 'Literal', value: source },
+        attributes: [],
+        ...overrides,
+    };
+}
+
+describe('Backend Functions - rejectNodeBuiltinImports', () => {
+    const filePath = '/project/src/math.backend.ts';
+
+    const allowedCases = [
+        {
+            description: 'allow importing a relative module',
+            source: './helpers',
+        },
+        {
+            description: 'allow importing a scoped npm package',
+            source: '@datadog/action-catalog',
+        },
+        {
+            description: 'allow importing an ordinary npm package',
+            source: 'lodash',
+        },
+    ];
+
+    test.each(allowedCases)('Should $description', ({ source }) => {
+        const ast = program([importDecl(source)]);
+        expect(() => rejectNodeBuiltinImports(ast, filePath)).not.toThrow();
+    });
+
+    const rejectedCases = [
+        {
+            description: 'reject importing "node:fs" via the node: prefix',
+            source: 'node:fs',
+        },
+        {
+            description: 'reject importing the bare built-in "fs"',
+            source: 'fs',
+        },
+        {
+            description: 'reject importing "child_process"',
+            source: 'child_process',
+        },
+        {
+            description: 'reject importing "node:child_process"',
+            source: 'node:child_process',
+        },
+        {
+            description: 'reject importing "net"',
+            source: 'net',
+        },
+        {
+            description: 'reject importing a built-in subpath "fs/promises"',
+            source: 'fs/promises',
+        },
+    ];
+
+    test.each(rejectedCases)('Should $description', ({ source }) => {
+        const ast = program([importDecl(source)]);
+        expect(() => rejectNodeBuiltinImports(ast, filePath)).toThrow(
+            `Importing Node built-in module "${source}" is not supported in .backend.ts files`,
+        );
+        expect(() => rejectNodeBuiltinImports(ast, filePath)).toThrow(filePath);
+    });
+
+    test('Should allow a type-only import of a Node built-in', () => {
+        // import type { Stats } from 'fs';
+        const ast = program([
+            importDecl('fs', { importKind: 'type' } as Partial<ImportDeclaration>),
+        ]);
+        expect(() => rejectNodeBuiltinImports(ast, filePath)).not.toThrow();
+    });
+
+    test('Should ignore non-import statements', () => {
+        const ast = program([
+            {
+                type: 'ExpressionStatement',
+                expression: { type: 'Literal', value: 1 },
+            },
+        ]);
+        expect(() => rejectNodeBuiltinImports(ast, filePath)).not.toThrow();
+    });
+});
diff --git a/packages/plugins/apps/src/backend/ast-parsing/reject-node-builtin-imports.ts b/packages/plugins/apps/src/backend/ast-parsing/reject-node-builtin-imports.ts
new file mode 100644
index 000000000..e39e5eab3
--- /dev/null
+++ b/packages/plugins/apps/src/backend/ast-parsing/reject-node-builtin-imports.ts
@@ -0,0 +1,44 @@
+// Unless explicitly stated otherwise all files in this repository are licensed under the MIT License.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2019-Present Datadog, Inc.
+
+import type { BaseNode } from 'estree';
+import { builtinModules } from 'node:module';
+
+import { ensureProgram, isTypeOnly } from './type-guards';
+
+const RESTRICTED_MODULES = new Set<string>(builtinModules);
+
+function isRestrictedSource(source: string): boolean {
+    return source.startsWith('node:') || RESTRICTED_MODULES.has(source);
+}
+
+/**
+ * Reject static imports of Node built-in modules in `.backend.ts` files.
+ * Backend functions run in a restricted environment with no direct Node
+ * built-in or network access — everything, including raw HTTP requests,
+ * must go through an Action Platform action ($.Actions or an
+ * @datadog/action-catalog typed wrapper).
+ *
+ * This is a best-effort, defense-in-depth check on static `import` specifiers
+ * only — it doesn't catch `require()` or dynamic `import()` of a computed
+ * specifier. See also `rejectRestrictedGlobals`, which covers bare network
+ * globals like `fetch` that need no import at all.
+ */
+export function rejectNodeBuiltinImports(ast: BaseNode, filePath: string): void {
+    const program = ensureProgram(ast, filePath);
+    for (const node of program.body) {
+        if (node.type !== 'ImportDeclaration' || isTypeOnly(node)) {
+            continue;
+        }
+
+        const source = node.source.value;
+        if (typeof source === 'string' && isRestrictedSource(source)) {
+            throw new Error(
+                `Importing Node built-in module "${source}" is not supported in .backend.ts files. ` +
+                    `Backend functions run in a restricted environment and must use an Action ` +
+                    `Platform action ($.Actions or an @datadog/action-catalog typed wrapper) instead: ${filePath}`,
+            );
+        }
+    }
+}
diff --git a/packages/plugins/apps/src/backend/ast-parsing/reject-restricted-globals.test.ts b/packages/plugins/apps/src/backend/ast-parsing/reject-restricted-globals.test.ts
new file mode 100644
index 000000000..d43ec70b7
--- /dev/null
+++ b/packages/plugins/apps/src/backend/ast-parsing/reject-restricted-globals.test.ts
@@ -0,0 +1,65 @@
+// Unless explicitly stated otherwise all files in this repository are licensed under the MIT License.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2019-Present Datadog, Inc.
+
+import { rejectRestrictedGlobals } from '@dd/apps-plugin/backend/ast-parsing/reject-restricted-globals';
+import { parseAst } from 'rollup/parseAst';
+
+describe('Backend Functions - rejectRestrictedGlobals', () => {
+    const filePath = '/project/src/math.backend.ts';
+
+    const rejectedCases = [
+        {
+            description: 'reject a bare fetch() call',
+            code: 'export async function run() { return fetch("https://example.com"); }',
+        },
+        {
+            description: 'reject fetch referenced without calling it',
+            code: 'export function run() { const f = fetch; return f; }',
+        },
+        {
+            description: 'reject new XMLHttpRequest()',
+            code: 'export function run() { return new XMLHttpRequest(); }',
+        },
+        {
+            description: 'reject new WebSocket(...)',
+            code: 'export function run() { return new WebSocket("wss://example.com"); }',
+        },
+        {
+            description: 'reject new EventSource(...)',
+            code: 'export function run() { return new EventSource("/events"); }',
+        },
+    ];
+
+    test.each(rejectedCases)('Should $description', ({ code }) => {
+        const ast = parseAst(code);
+        expect(() => rejectRestrictedGlobals(ast, filePath)).toThrow(
+            'is not supported in .backend.ts files',
+        );
+        expect(() => rejectRestrictedGlobals(ast, filePath)).toThrow(filePath);
+    });
+
+    const allowedCases = [
+        {
+            description: 'allow calling an imported action-catalog function',
+            code: "import { request } from '@datadog/action-catalog/http/http';\nexport async function run() { return request({ inputs: {} }); }",
+        },
+        {
+            description: 'allow a locally-declared function that happens to be named fetch',
+            code: 'function fetch() { return "local"; }\nexport function run() { return fetch(); }',
+        },
+        {
+            description: 'allow a parameter named fetch shadowing the global',
+            code: 'export function run(fetch) { return fetch(); }',
+        },
+        {
+            description: 'allow unrelated code with no restricted-global references',
+            code: 'export function run(a, b) { return a + b; }',
+        },
+    ];
+
+    test.each(allowedCases)('Should $description', ({ code }) => {
+        const ast = parseAst(code);
+        expect(() => rejectRestrictedGlobals(ast, filePath)).not.toThrow();
+    });
+});
diff --git a/packages/plugins/apps/src/backend/ast-parsing/reject-restricted-globals.ts b/packages/plugins/apps/src/backend/ast-parsing/reject-restricted-globals.ts
new file mode 100644
index 000000000..f7a3b8bd6
--- /dev/null
+++ b/packages/plugins/apps/src/backend/ast-parsing/reject-restricted-globals.ts
@@ -0,0 +1,53 @@
+// Unless explicitly stated otherwise all files in this repository are licensed under the MIT License.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2019-Present Datadog, Inc.
+
+import type { BaseNode } from 'estree';
+
+import { analyzeModuleScope } from './module-scope';
+import { ensureProgram } from './type-guards';
+
+const RESTRICTED_GLOBALS = new Set(['fetch', 'XMLHttpRequest', 'WebSocket', 'EventSource']);
+
+/**
+ * Reject references to network-capable globals in `.backend.ts` files.
+ * Backend functions have no raw network access under today's v1 runtime —
+ * Deno's `--allow-net` is off — so any outbound call must go through an
+ * Action Platform action (`$.Actions` or an `@datadog/action-catalog` typed
+ * wrapper), never a direct HTTP client. Import-specifier restriction alone
+ * can't catch this: these are bare globals, not imports.
+ *
+ * This is the enforcement layer for a trap that's easy to fall into
+ * otherwise: `fetch` works fine during local dev (nothing stopped it before
+ * this check existed) but fails once the app is actually published, since
+ * production's sandbox blocks it. A separate, complementary effort adds
+ * AI-authoring guidance steering generated code away from `fetch` in the
+ * first place — that reduces how often this gets written at all, but only
+ * this build-time check actually guarantees it never ships, regardless of
+ * whether the code came from an AI, a human, or a copy-pasted snippet.
+ *
+ * Backend functions' planned v2 (Terrapin-based) sandbox will lift this
+ * restriction — legacy (pre-v2) apps are the ones that need it.
+ *
+ * This is a best-effort, defense-in-depth check: it flags any reference to one
+ * of these names that eslint-scope can't resolve to a declaration in this
+ * module (i.e. it falls through to the ambient global instead of a local
+ * variable or import that happens to share the name).
+ */
+export function rejectRestrictedGlobals(ast: BaseNode, filePath: string): void {
+    const program = ensureProgram(ast, filePath);
+    const scopeAnalysis = analyzeModuleScope(program);
+
+    for (const [identifier, reference] of scopeAnalysis.referencesByIdentifier) {
+        if (!RESTRICTED_GLOBALS.has(identifier.name) || reference.resolved) {
+            continue;
+        }
+
+        throw new Error(
+            `Using "${identifier.name}" is not supported in .backend.ts files. ` +
+                `Backend functions cannot make raw network requests in production — ` +
+                `use an Action Platform action ($.Actions or an @datadog/action-catalog ` +
+                `typed wrapper) instead: ${filePath}`,
+        );
+    }
+}
diff --git a/packages/plugins/apps/src/vite/index.test.ts b/packages/plugins/apps/src/vite/index.test.ts
index 3a798312f..debb6b72e 100644
--- a/packages/plugins/apps/src/vite/index.test.ts
+++ b/packages/plugins/apps/src/vite/index.test.ts
@@ -160,6 +160,31 @@ describe('Backend Functions - getVitePlugin', () => {
         expect(assets.collectAssets).toHaveBeenCalledWith(['dist/**/*'], '/build');
     });
 
+    test('Should reject a backend file importing a Node built-in module', () => {
+        const plugin = getVitePlugin(defaultOptions);
+        const transform = plugin!.transform as {
+            handler: (code: string, id: string) => unknown;
+        };
+
+        expect(() =>
+            transform.handler.call(
+                {
+                    parse: parseAst,
+                    resolve: jest.fn(async () => null),
+                    load: jest.fn(async () => null),
+                    addWatchFile: jest.fn(),
+                },
+                `
+                    import fs from 'node:fs';
+                    export function myHandler() {
+                        return fs.readFileSync('/etc/passwd', 'utf8');
+                    }
+                `,
+                '/build/src/backend/myHandler.backend.ts',
+            ),
+        ).toThrow('Importing Node built-in module "node:fs" is not supported in .backend.ts files');
+    });
+
     test('Should inject the apps runtime', () => {
         getVitePlugin(defaultOptions);
 
diff --git a/packages/plugins/apps/src/vite/index.ts b/packages/plugins/apps/src/vite/index.ts
index 831ce75c2..9e4cf3a96 100644
--- a/packages/plugins/apps/src/vite/index.ts
+++ b/packages/plugins/apps/src/vite/index.ts
@@ -14,6 +14,8 @@ import {
     type DoAuthenticatedRequest,
 } from '../auth';
 import { extractExportedFunctions } from '../backend/ast-parsing/extract-backend-functions';
+import { rejectNodeBuiltinImports } from '../backend/ast-parsing/reject-node-builtin-imports';
+import { rejectRestrictedGlobals } from '../backend/ast-parsing/reject-restricted-globals';
 import { encodeQueryName } from '../backend/encodeQueryName';
 import { generateProxyModule } from '../backend/proxy-codegen';
 import type { BackendFunction } from '../backend/types';
@@ -130,6 +132,8 @@ export const getVitePlugin = ({
             // frontend proxy that calls executeBackendFunction at runtime.
             handler(code, id) {
                 const ast = this.parse(code);
+                rejectNodeBuiltinImports(ast, id);
+                rejectRestrictedGlobals(ast, id);
                 const exportNames = extractExportedFunctions(ast, id);
                 if (exportNames.length === 0) {
                     log.warn(