fix(slack): harden native webhook configuration

apps/docs/content/docs/platform/self-hosting/integrations-oauth.mdx

@@ -196,6 +196,8 @@ Webhook triggers receive callbacks from the provider and must be able to verify
 | `SLACK_SIGNING_SECRET` | Verifying Slack event and slash-command signatures |
 | `SLACK_EXTENDED_SCOPES` / `NEXT_PUBLIC_SLACK_EXTENDED_SCOPES` | Enabling the native Sim-app trigger and its broader Slack scope set; set both to the same value |
 
+When enabling the native Sim Slack trigger, configure all three variables together. Enable the extended-scope flags only after Slack approves the app for `assistant:write`, `app_mentions:read`, and `im:history`; otherwise Slack rejects OAuth authorization. Slack OAuth actions can use `SLACK_CLIENT_ID` and `SLACK_CLIENT_SECRET` without enabling the native trigger or supplying a signing secret.
+
 Your deployment must also be reachable from the provider's servers for webhook triggers to fire — a Sim instance on a private network can use polling triggers but not webhook triggers. Polling triggers additionally require the scheduler; see [Background Jobs](/platform/self-hosting/background-jobs).
 
 <FAQ items={[

apps/sim/app/api/webhooks/slack/route.test.ts

@@ -4,12 +4,19 @@
 import { resetEnvMock, setEnv } from '@sim/testing'
 import { afterAll, beforeEach, describe, expect, it, vi } from 'vitest'
 
-const { mockParseWebhookBody, mockFindWebhooksByRoutingKey, mockDispatchResolvedWebhookTarget } =
-  vi.hoisted(() => ({
-    mockParseWebhookBody: vi.fn(),
-    mockFindWebhooksByRoutingKey: vi.fn(),
-    mockDispatchResolvedWebhookTarget: vi.fn(),
-  }))
+const {
+  mockParseWebhookBody,
+  mockFindWebhooksByRoutingKey,
+  mockDispatchResolvedWebhookTarget,
+  mockHandleSlackChallenge,
+  mockVerifySlackRequestSignature,
+} = vi.hoisted(() => ({
+  mockParseWebhookBody: vi.fn(),
+  mockFindWebhooksByRoutingKey: vi.fn(),
+  mockDispatchResolvedWebhookTarget: vi.fn(),
+  mockHandleSlackChallenge: vi.fn(),
+  mockVerifySlackRequestSignature: vi.fn(),
+}))
 
 vi.mock('@/lib/core/admission/gate', () => ({
   tryAdmit: () => ({ release: vi.fn() }),
@@ -23,8 +30,8 @@ vi.mock('@/lib/webhooks/processor', () => ({
 }))
 
 vi.mock('@/lib/webhooks/providers/slack', () => ({
-  handleSlackChallenge: () => null,
-  verifySlackRequestSignature: () => null,
+  handleSlackChallenge: mockHandleSlackChallenge,
+  verifySlackRequestSignature: mockVerifySlackRequestSignature,
   resolveSlackEventKey: () => null,
 }))
 
@@ -60,6 +67,8 @@ describe('Slack app webhook route', () => {
   beforeEach(() => {
     vi.clearAllMocks()
     setEnv({ SLACK_SIGNING_SECRET: 'test-secret' })
+    mockHandleSlackChallenge.mockReturnValue(null)
+    mockVerifySlackRequestSignature.mockReturnValue(null)
     mockFindWebhooksByRoutingKey.mockResolvedValue([webhook('wh1')])
     mockDispatchResolvedWebhookTarget.mockResolvedValue({
       outcome: 'queued',
@@ -70,9 +79,63 @@ describe('Slack app webhook route', () => {
 
   it('dispatches each webhook resolved for the event team', async () => {
     await run(messageBody)
+    expect(mockVerifySlackRequestSignature).toHaveBeenCalledWith(
+      'test-secret',
+      expect.anything(),
+      JSON.stringify(messageBody),
+      expect.any(String)
+    )
     expect(mockDispatchResolvedWebhookTarget).toHaveBeenCalledTimes(1)
   })
 
+  it('rejects a verification challenge when the native app is not configured', async () => {
+    setEnv({ SLACK_SIGNING_SECRET: undefined })
+    mockHandleSlackChallenge.mockReturnValue(new Response('challenge', { status: 200 }))
+
+    const response = await run({ type: 'url_verification', challenge: 'challenge' })
+
+    expect(response.status).toBe(500)
+    expect(mockVerifySlackRequestSignature).not.toHaveBeenCalled()
+    expect(mockHandleSlackChallenge).not.toHaveBeenCalled()
+  })
+
+  it('treats a whitespace-only native signing secret as unconfigured', async () => {
+    setEnv({ SLACK_SIGNING_SECRET: '   ' })
+
+    const response = await run(messageBody)
+
+    expect(response.status).toBe(500)
+    expect(mockVerifySlackRequestSignature).not.toHaveBeenCalled()
+    expect(mockFindWebhooksByRoutingKey).not.toHaveBeenCalled()
+  })
+
+  it('verifies a signed request before answering the verification challenge', async () => {
+    const body = { type: 'url_verification', challenge: 'challenge' }
+    mockHandleSlackChallenge.mockReturnValue(new Response('challenge', { status: 200 }))
+
+    const response = await run(body)
+
+    expect(mockVerifySlackRequestSignature).toHaveBeenCalledWith(
+      'test-secret',
+      expect.anything(),
+      JSON.stringify(body),
+      expect.any(String)
+    )
+    expect(mockHandleSlackChallenge).toHaveBeenCalledWith(body)
+    expect(response.status).toBe(200)
+    expect(mockFindWebhooksByRoutingKey).not.toHaveBeenCalled()
+  })
+
+  it('does not answer a verification challenge with an invalid signature', async () => {
+    mockVerifySlackRequestSignature.mockReturnValue(new Response(null, { status: 401 }))
+    mockHandleSlackChallenge.mockReturnValue(new Response('challenge', { status: 200 }))
+
+    const response = await run({ type: 'url_verification', challenge: 'challenge' })
+
+    expect(response.status).toBe(401)
+    expect(mockHandleSlackChallenge).not.toHaveBeenCalled()
+  })
+
   it('continues cleanly when the dispatcher filters the event', async () => {
     mockDispatchResolvedWebhookTarget.mockResolvedValue({
       outcome: 'ignored',

apps/sim/app/api/webhooks/slack/route.ts

@@ -1,12 +1,12 @@
 import { createLogger } from '@sim/logger'
 import { type NextRequest, NextResponse } from 'next/server'
 import { admissionRejectedResponse, tryAdmit } from '@/lib/core/admission/gate'
-import { env } from '@/lib/core/config/env'
 import { generateRequestId } from '@/lib/core/utils/request'
 import { withRouteHandler } from '@/lib/core/utils/with-route-handler'
 import { findWebhooksByRoutingKey, parseWebhookBody } from '@/lib/webhooks/processor'
 import { handleSlackChallenge, verifySlackRequestSignature } from '@/lib/webhooks/providers/slack'
 import { dispatchSlackWebhooks, getSlackDispatchResponse } from '@/lib/webhooks/slack-dispatch'
+import { getSlackNativeSigningSecret } from '@/lib/webhooks/slack-native-config'
 
 const logger = createLogger('SlackAppWebhookAPI')
 
@@ -44,13 +44,7 @@ async function handleSlackAppWebhook(request: NextRequest): Promise<NextResponse
   }
   const { body, rawBody } = parseResult
 
-  // Slack's endpoint verification handshake — echo the challenge back.
-  const challenge = handleSlackChallenge(body)
-  if (challenge) {
-    return challenge
-  }
-
-  const signingSecret = env.SLACK_SIGNING_SECRET
+  const signingSecret = getSlackNativeSigningSecret()
   if (!signingSecret) {
     logger.error(`[${requestId}] SLACK_SIGNING_SECRET is not configured`)
     return new NextResponse('Slack app not configured', { status: 500 })
@@ -61,6 +55,11 @@ async function handleSlackAppWebhook(request: NextRequest): Promise<NextResponse
     return authError
   }
 
+  const challenge = handleSlackChallenge(body)
+  if (challenge) {
+    return challenge
+  }
+
   const payload = body as Record<string, unknown>
 
   // Route by the installed workspace(s). For Slack Connect the outer `team_id`

apps/sim/lib/webhooks/deploy.test.ts

@@ -7,6 +7,8 @@ import {
   queueTableRows,
   resetDbChainMock,
   resetEnvFlagsMock,
+  resetEnvMock,
+  setEnv,
   setEnvFlags,
 } from '@sim/testing'
 import { eq, ne } from 'drizzle-orm'
@@ -84,6 +86,7 @@ import { getTrigger } from '@/triggers'
 
 afterAll(() => {
   resetDbChainMock()
+  resetEnvMock()
   resetEnvFlagsMock()
 })
 
@@ -151,6 +154,7 @@ function makeBlock(
 beforeEach(() => {
   vi.clearAllMocks()
   resetDbChainMock()
+  setEnv({ SLACK_SIGNING_SECRET: 'test-secret' })
   setEnvFlags({ isSlackExtendedScopesEnabled: true })
   ;(getProviderHandler as unknown as Mock).mockImplementation((provider: string) =>
     provider === 'quickbooks' ? quickBooksHandler : {}
@@ -301,8 +305,9 @@ describe('resolveWebhookConfigForBlock — slack_oauth routing', () => {
     })
   }
 
-  it('routes a custom bot credential by credential id on the slack provider', async () => {
+  it('routes a custom bot credential without the native app signing secret', async () => {
     setEnvFlags({ isSlackExtendedScopesEnabled: false })
+    setEnv({ SLACK_SIGNING_SECRET: undefined })
     mockGetSlackBotCredential.mockResolvedValue({
       workspaceId: 'ws-1',
       botToken: 'xoxb-token',
@@ -403,6 +408,24 @@ describe('resolveWebhookConfigForBlock — slack_oauth routing', () => {
     expect(mockFetchSlackTeamId).not.toHaveBeenCalled()
   })
 
+  it('rejects a Sim-app credential when its signing secret is not configured', async () => {
+    setEnv({ SLACK_SIGNING_SECRET: undefined })
+    mockGetSlackBotCredential.mockResolvedValue(null)
+    mockResolveOAuthAccountId.mockResolvedValue({ accountId: 'acct-1' })
+
+    const result = await resolveSlack({ eventType: 'message', customBotCredential: 'cred_oauth_1' })
+
+    expect(result?.success).toBe(false)
+    if (result?.success) throw new Error('expected failure')
+    expect(result?.error).toEqual({
+      message:
+        'The Sim Slack app trigger is not configured for this deployment. Configure its signing secret or select a custom bot.',
+      status: 400,
+    })
+    expect(mockRefreshAccessTokenIfNeeded).not.toHaveBeenCalled()
+    expect(mockFetchSlackTeamId).not.toHaveBeenCalled()
+  })
+
   it('rejects a custom bot credential from another workspace', async () => {
     mockGetSlackBotCredential.mockResolvedValue({
       workspaceId: 'other-ws',

apps/sim/lib/webhooks/deploy.ts

@@ -28,6 +28,7 @@ import {
   type StableDesiredWebhookRegistration,
 } from '@/lib/webhooks/registration-service'
 import { LEGACY_SLACK_CUSTOM_BOT_INGRESS_MODE } from '@/lib/webhooks/slack-custom-ingress-constants'
+import { getSlackNativeSigningSecret } from '@/lib/webhooks/slack-native-config'
 import {
   isSlackStreamResponseRequested,
   normalizeSlackStreamResponseConfig,
@@ -517,6 +518,16 @@ export async function resolveWebhookConfigForBlock(input: {
           },
         }
       }
+      if (!getSlackNativeSigningSecret()) {
+        return {
+          success: false,
+          error: {
+            message:
+              'The Sim Slack app trigger is not configured for this deployment. Configure its signing secret or select a custom bot.',
+            status: 400,
+          },
+        }
+      }
       if (isSlackStreamResponseRequested(providerConfig)) {
         return {
           success: false,

apps/sim/lib/webhooks/providers/slack.test.ts

@@ -1,3 +1,4 @@
+import { createHmac } from 'node:crypto'
 import { describe, expect, it } from 'vitest'
 import {
   handleSlackChallenge,
@@ -23,6 +24,66 @@ describe('slackHandler responses', () => {
   })
 })
 
+describe('slackHandler request verification', () => {
+  const rawBody = JSON.stringify({ type: 'event_callback' })
+
+  function signedRequest(signingSecret: string, timestamp: string, body = rawBody): Request {
+    const signature = createHmac('sha256', signingSecret)
+      .update(`v0:${timestamp}:${body}`, 'utf8')
+      .digest('hex')
+    return new Request('https://sim.test/api/webhooks/trigger/slack', {
+      method: 'POST',
+      headers: {
+        'x-slack-request-timestamp': timestamp,
+        'x-slack-signature': `v0=${signature}`,
+      },
+    })
+  }
+
+  function verify(request: Request, providerConfig: Record<string, unknown>, body = rawBody) {
+    return slackHandler.verifyAuth!({
+      webhook: {},
+      workflow: {},
+      request: request as unknown as import('next/server').NextRequest,
+      rawBody: body,
+      requestId: 'slack-auth-test',
+      providerConfig,
+    })
+  }
+
+  it('fails closed when a legacy Slack webhook has no signing secret', async () => {
+    const response = await verify(new Request('https://sim.test'), {})
+
+    expect(response?.status).toBe(401)
+  })
+
+  it('accepts a correctly signed current request', async () => {
+    const signingSecret = 'test-signing-secret'
+    const timestamp = String(Math.floor(Date.now() / 1000))
+
+    expect(verify(signedRequest(signingSecret, timestamp), { signingSecret })).toBeNull()
+  })
+
+  it('rejects a signature computed for different raw bytes', async () => {
+    const signingSecret = 'test-signing-secret'
+    const timestamp = String(Math.floor(Date.now() / 1000))
+    const request = signedRequest(signingSecret, timestamp)
+
+    const response = await verify(request, { signingSecret }, `${rawBody} `)
+
+    expect(response?.status).toBe(401)
+  })
+
+  it("rejects an otherwise valid signature outside Slack's five-minute replay window", async () => {
+    const signingSecret = 'test-signing-secret'
+    const timestamp = String(Math.floor(Date.now() / 1000) - 301)
+
+    const response = await verify(signedRequest(signingSecret, timestamp), { signingSecret })
+
+    expect(response?.status).toBe(401)
+  })
+})
+
 describe('slackHandler formatInput - Events API', () => {
   it('maps an app_mention event', async () => {
     const { input } = await slackHandler.formatInput!(

apps/sim/lib/webhooks/providers/slack.ts

@@ -840,7 +840,8 @@ export const slackHandler: WebhookProviderHandler = {
   verifyAuth({ request, rawBody, requestId, providerConfig }: AuthContext) {
     const signingSecret = providerConfig.signingSecret as string | undefined
     if (!signingSecret) {
-      return null
+      logger.warn(`[${requestId}] Slack webhook signing secret not configured`)
+      return new NextResponse('Unauthorized - Missing Slack signing secret', { status: 401 })
     }
     return verifySlackRequestSignature(signingSecret, request, rawBody, requestId)
   },

apps/sim/lib/webhooks/slack-native-config.ts

@@ -0,0 +1,7 @@
+import { env } from '@/lib/core/config/env'
+
+/** Returns the signing secret for the native Sim Slack app when it is configured. */
+export function getSlackNativeSigningSecret(): string | null {
+  const signingSecret = env.SLACK_SIGNING_SECRET?.trim()
+  return signingSecret || null
+}