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fix(api): constrain workflow response headers (#8341)
* fix(api): constrain workflow response headers * fix(api): reserve additional browser policy headers
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‎apps/docs/content/docs/workflows/blocks/response.mdx‎

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@@ -52,6 +52,8 @@ Extra response headers, as key-value pairs:
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| Cache-Control | no-cache |
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| X-API-Version | 1.0 |
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HTTP responses always use `Content-Type: application/json` and `X-Content-Type-Options: nosniff`. Headers that set cookies, redirect the browser, change security or CORS policies, or control the HTTP transport are ignored. Ordinary custom headers and cache directives are preserved.
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## Outputs
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A Response block is a terminal block, so nothing reads from it. Its `data`, `status`, and `headers` become the HTTP response itself. A workflow with no Response block returns its last block's output by default; add a Response block when you need exact HTTP control.

‎apps/sim/lib/workflows/response-security.test.ts‎

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import { describe, expect, it } from 'vitest'
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import { createHttpResponseFromBlock } from '@/lib/workflows/utils'
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describe('workflow HTTP response safety', () => {
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it.each([
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{ 'Content-Type': 'text/html' },
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{ 'content-type': 'text/html' },
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{ 'CoNtEnT-TyPe': 'image/svg+xml' },
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{ 'Content-Type': 'application/json', 'content-type': 'text/html' },
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])('keeps untrusted markup as JSON with headers %j', async (headers) => {
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const data = { message: '<script>alert(document.domain)</script>' }
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const response = await createHttpResponseFromBlock({
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output: {
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data,
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status: 201,
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headers: {
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...headers,
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'X-Content-Type-Options': 'invalid',
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'X-API-Version': '1.0',
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'Cache-Control': 'no-cache',
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'Retry-After': '30',
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},
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},
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})
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expect(response.headers.get('content-type')).toBe('application/json')
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expect(response.headers.get('x-content-type-options')).toBe('nosniff')
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expect(response.status).toBe(201)
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expect(response.headers.get('x-api-version')).toBe('1.0')
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expect(response.headers.get('cache-control')).toBe('no-cache')
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expect(response.headers.get('retry-after')).toBe('30')
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expect(await response.json()).toEqual(data)
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})
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it('does not let workflow output set cookies, browser policies, redirects, or transport headers', async () => {
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const response = await createHttpResponseFromBlock({
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output: {
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data: { message: 'complete' },
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status: 200,
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headers: {
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'SeT-CoOkIe': 'session=untrusted; Path=/',
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'Set-Cookie2': 'session=untrusted',
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'Content-Disposition': 'inline',
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'Content-Security-Policy': "default-src * 'unsafe-inline'",
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'Content-Security-Policy-Report-Only': 'report-uri /untrusted',
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'X-Frame-Options': 'ALLOWALL',
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'X-XSS-Protection': '0',
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'X-Download-Options': 'untrusted',
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'X-DNS-Prefetch-Control': 'on',
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'X-Permitted-Cross-Domain-Policies': 'all',
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'X-UA-Compatible': 'IE=7',
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'X-WebKit-CSP': "default-src * 'unsafe-inline'",
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'X-Content-Security-Policy': "default-src * 'unsafe-inline'",
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'Accept-CH': 'Sec-CH-UA-Model',
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'Accept-CH-Lifetime': '86400',
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'Critical-CH': 'Sec-CH-UA-Model',
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'Public-Key-Pins': 'max-age=0',
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'Public-Key-Pins-Report-Only': 'max-age=0; report-uri="/untrusted"',
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'Access-Control-Allow-Origin': '*',
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'Access-Control-Allow-Credentials': 'true',
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'Cross-Origin-Resource-Policy': 'cross-origin',
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'Clear-Site-Data': '"*"',
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'Permissions-Policy': 'camera=*',
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'Document-Policy': 'force-load-at-top',
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'Referrer-Policy': 'unsafe-url',
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'Strict-Transport-Security': 'max-age=0',
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'Origin-Agent-Cluster': '?0',
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Location: '/untrusted',
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Refresh: '0; url=/untrusted',
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Link: '</untrusted>; rel=preload; as=script',
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'Report-To': '{"group":"untrusted"}',
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'Reporting-Endpoints': 'default="/untrusted"',
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NEL: '{"report_to":"untrusted","max_age":3600}',
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'Content-Length': '1',
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'Content-Encoding': 'gzip',
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'Transfer-Encoding': 'chunked',
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Connection: 'close',
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'X-Middleware-Rewrite': '/untrusted',
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'X-Accel-Redirect': '/untrusted',
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'X-Sendfile': '/untrusted',
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},
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},
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})
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expect(Object.fromEntries(response.headers)).toEqual({
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'content-type': 'application/json',
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'x-content-type-options': 'nosniff',
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})
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expect(await response.json()).toEqual({ message: 'complete' })
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})
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})

‎apps/sim/lib/workflows/utils.ts‎

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@@ -293,17 +293,80 @@ export const workflowHasResponseBlock = (
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return responseBlock !== undefined
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}
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/** Headers that control the app origin or HTTP transport belong to the server. */
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const RESERVED_RESPONSE_HEADERS = new Set([
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'accept-ch',
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'accept-ch-lifetime',
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'alt-svc',
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'clear-site-data',
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'connection',
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'content-disposition',
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'content-encoding',
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'content-length',
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'content-location',
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'content-range',
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'critical-ch',
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'document-policy',
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'keep-alive',
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'link',
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'location',
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'nel',
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'origin-agent-cluster',
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'permissions-policy',
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'proxy-authenticate',
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'public-key-pins',
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'public-key-pins-report-only',
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'referrer-policy',
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'refresh',
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'report-to',
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'reporting-endpoints',
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'set-cookie',
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'set-cookie2',
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'strict-transport-security',
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'trailer',
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'transfer-encoding',
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'upgrade',
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'www-authenticate',
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'x-content-security-policy',
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'x-dns-prefetch-control',
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'x-download-options',
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'x-frame-options',
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'x-permitted-cross-domain-policies',
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'x-sendfile',
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'x-ua-compatible',
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'x-webkit-csp',
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'x-xss-protection',
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])
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const RESERVED_RESPONSE_HEADER_PREFIXES = [
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'access-control-',
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'content-security-policy',
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'cross-origin-',
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'sec-',
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'x-accel-',
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'x-middleware-',
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] as const
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export const createHttpResponseFromBlock = async (
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executionResult: Pick<ExecutionResult, 'output'>,
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context?: ExecutionMaterializationContext
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): Promise<NextResponse> => {
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const { data = {}, status = 200, headers = {} } = executionResult.output
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const responseData = await materializeInlineExecutionValue(data, context)
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const responseHeaders = new Headers({
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'Content-Type': 'application/json',
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...headers,
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})
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const responseHeaders = new Headers()
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for (const [name, value] of new Headers(headers)) {
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if (
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!RESERVED_RESPONSE_HEADERS.has(name) &&
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!RESERVED_RESPONSE_HEADER_PREFIXES.some((prefix) => name.startsWith(prefix))
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) {
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responseHeaders.set(name, value)
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}
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}
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// JSON serialization does not escape HTML; enforce the MIME type after normalizing header names.
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responseHeaders.set('Content-Type', 'application/json')
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responseHeaders.set('X-Content-Type-Options', 'nosniff')
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return NextResponse.json(responseData, {
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status: status,

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