feat(mcp): add ALLOWED_MCP_DOMAINS env var for domain allowlist

Author: waleedlatif1

apps/sim/app/api/mcp/servers/[id]/route.ts

@@ -3,6 +3,7 @@ import { mcpServers } from '@sim/db/schema'
 import { createLogger } from '@sim/logger'
 import { and, eq, isNull } from 'drizzle-orm'
 import type { NextRequest } from 'next/server'
+import { McpDomainNotAllowedError, validateMcpDomain } from '@/lib/mcp/domain-check'
 import { getParsedBody, withMcpAuth } from '@/lib/mcp/middleware'
 import { mcpService } from '@/lib/mcp/service'
 import { createMcpErrorResponse, createMcpSuccessResponse } from '@/lib/mcp/utils'
@@ -29,6 +30,17 @@ export const PATCH = withMcpAuth<{ id: string }>('write')(
       // Remove workspaceId from body to prevent it from being updated
       const { workspaceId: _, ...updateData } = body
 
+      if (updateData.url) {
+        try {
+          validateMcpDomain(updateData.url)
+        } catch (e) {
+          if (e instanceof McpDomainNotAllowedError) {
+            return createMcpErrorResponse(e, e.message, 403)
+          }
+          throw e
+        }
+      }
+
       // Get the current server to check if URL is changing
       const [currentServer] = await db
         .select({ url: mcpServers.url })

apps/sim/app/api/mcp/servers/route.ts

@@ -3,6 +3,7 @@ import { mcpServers } from '@sim/db/schema'
 import { createLogger } from '@sim/logger'
 import { and, eq, isNull } from 'drizzle-orm'
 import type { NextRequest } from 'next/server'
+import { McpDomainNotAllowedError, validateMcpDomain } from '@/lib/mcp/domain-check'
 import { getParsedBody, withMcpAuth } from '@/lib/mcp/middleware'
 import { mcpService } from '@/lib/mcp/service'
 import {
@@ -72,6 +73,15 @@ export const POST = withMcpAuth('write')(
         )
       }
 
+      try {
+        validateMcpDomain(body.url)
+      } catch (e) {
+        if (e instanceof McpDomainNotAllowedError) {
+          return createMcpErrorResponse(e, e.message, 403)
+        }
+        throw e
+      }
+
       const serverId = body.url ? generateMcpServerId(workspaceId, body.url) : crypto.randomUUID()
 
       const [existingServer] = await db

apps/sim/app/api/mcp/servers/test-connection/route.ts

@@ -1,6 +1,7 @@
 import { createLogger } from '@sim/logger'
 import type { NextRequest } from 'next/server'
 import { McpClient } from '@/lib/mcp/client'
+import { McpDomainNotAllowedError, validateMcpDomain } from '@/lib/mcp/domain-check'
 import { getParsedBody, withMcpAuth } from '@/lib/mcp/middleware'
 import { resolveMcpConfigEnvVars } from '@/lib/mcp/resolve-config'
 import type { McpTransport } from '@/lib/mcp/types'
@@ -71,6 +72,15 @@ export const POST = withMcpAuth('write')(
         )
       }
 
+      try {
+        validateMcpDomain(body.url)
+      } catch (e) {
+        if (e instanceof McpDomainNotAllowedError) {
+          return createMcpErrorResponse(e, e.message, 403)
+        }
+        throw e
+      }
+
       // Build initial config for resolution
       const initialConfig = {
         id: `test-${requestId}`,

apps/sim/app/api/settings/allowed-mcp-domains/route.ts

@@ -0,0 +1,21 @@
+import { NextResponse } from 'next/server'
+import { getAllowedMcpDomainsFromEnv } from '@/lib/core/config/feature-flags'
+import { getBaseUrl } from '@/lib/core/utils/urls'
+
+export async function GET() {
+  const configuredDomains = getAllowedMcpDomainsFromEnv()
+  if (configuredDomains === null) {
+    return NextResponse.json({ allowedMcpDomains: null })
+  }
+
+  try {
+    const platformHostname = new URL(getBaseUrl()).hostname.toLowerCase()
+    if (!configuredDomains.includes(platformHostname)) {
+      return NextResponse.json({
+        allowedMcpDomains: [...configuredDomains, platformHostname],
+      })
+    }
+  } catch {}
+
+  return NextResponse.json({ allowedMcpDomains: configuredDomains })
+}

apps/sim/app/workspace/[workspaceId]/w/components/sidebar/components/settings-modal/components/mcp/mcp.tsx

@@ -106,6 +106,21 @@ interface McpServer {
 
 const logger = createLogger('McpSettings')
 
+/**
+ * Checks if a URL's hostname is in the allowed domains list.
+ * Returns true if no allowlist is configured (null) or the domain matches.
+ */
+function isDomainAllowed(url: string | undefined, allowedDomains: string[] | null): boolean {
+  if (allowedDomains === null) return true
+  if (!url) return true
+  try {
+    const hostname = new URL(url).hostname.toLowerCase()
+    return allowedDomains.includes(hostname)
+  } catch {
+    return true
+  }
+}
+
 const DEFAULT_FORM_DATA: McpServerFormData = {
   name: '',
   transport: 'streamable-http',
@@ -390,6 +405,15 @@ export function MCP({ initialServerId }: MCPProps) {
   } = useMcpServerTest()
   const availableEnvVars = useAvailableEnvVarKeys(workspaceId)
 
+  const [allowedMcpDomains, setAllowedMcpDomains] = useState<string[] | null>(null)
+
+  useEffect(() => {
+    fetch('/api/settings/allowed-mcp-domains')
+      .then((res) => res.json())
+      .then((data) => setAllowedMcpDomains(data.allowedMcpDomains ?? null))
+      .catch(() => setAllowedMcpDomains(null))
+  }, [])
+
   const urlInputRef = useRef<HTMLInputElement>(null)
 
   const [showAddForm, setShowAddForm] = useState(false)
@@ -1006,10 +1030,12 @@ export function MCP({ initialServerId }: MCPProps) {
   const showNoResults = searchTerm.trim() && filteredServers.length === 0 && servers.length > 0
 
   const isFormValid = formData.name.trim() && formData.url?.trim()
-  const isSubmitDisabled = serversLoading || isAddingServer || !isFormValid
+  const isAddDomainBlocked = !isDomainAllowed(formData.url, allowedMcpDomains)
+  const isSubmitDisabled = serversLoading || isAddingServer || !isFormValid || isAddDomainBlocked
   const testButtonLabel = getTestButtonLabel(testResult, isTestingConnection)
 
   const isEditFormValid = editFormData.name.trim() && editFormData.url?.trim()
+  const isEditDomainBlocked = !isDomainAllowed(editFormData.url, allowedMcpDomains)
   const editTestButtonLabel = getTestButtonLabel(editTestResult, isEditTestingConnection)
   const hasEditChanges = useMemo(() => {
     if (editFormData.name !== editOriginalData.name) return true
@@ -1299,6 +1325,11 @@ export function MCP({ initialServerId }: MCPProps) {
                     onChange={(e) => handleEditInputChange('url', e.target.value)}
                     onScroll={setEditUrlScrollLeft}
                   />
+                  {isEditDomainBlocked && (
+                    <p className='mt-[4px] text-[12px] text-[var(--text-error)]'>
+                      Domain not permitted by server policy
+                    </p>
+                  )}
                 </FormField>
 
                 <div className='flex flex-col gap-[8px]'>
@@ -1351,7 +1382,7 @@ export function MCP({ initialServerId }: MCPProps) {
                 <Button
                   variant='default'
                   onClick={handleEditTestConnection}
-                  disabled={isEditTestingConnection || !isEditFormValid}
+                  disabled={isEditTestingConnection || !isEditFormValid || isEditDomainBlocked}
                 >
                   {editTestButtonLabel}
                 </Button>
@@ -1361,7 +1392,9 @@ export function MCP({ initialServerId }: MCPProps) {
                   </Button>
                   <Button
                     onClick={handleSaveEdit}
-                    disabled={!hasEditChanges || isUpdatingServer || !isEditFormValid}
+                    disabled={
+                      !hasEditChanges || isUpdatingServer || !isEditFormValid || isEditDomainBlocked
+                    }
                     variant='tertiary'
                   >
                     {isUpdatingServer ? 'Saving...' : 'Save'}
@@ -1434,6 +1467,11 @@ export function MCP({ initialServerId }: MCPProps) {
                   onChange={(e) => handleInputChange('url', e.target.value)}
                   onScroll={(scrollLeft) => handleUrlScroll(scrollLeft)}
                 />
+                {isAddDomainBlocked && (
+                  <p className='mt-[4px] text-[12px] text-[var(--text-error)]'>
+                    Domain not permitted by server policy
+                  </p>
+                )}
               </FormField>
 
               <div className='flex flex-col gap-[8px]'>
@@ -1479,7 +1517,7 @@ export function MCP({ initialServerId }: MCPProps) {
                 <Button
                   variant='default'
                   onClick={handleTestConnection}
-                  disabled={isTestingConnection || !isFormValid}
+                  disabled={isTestingConnection || !isFormValid || isAddDomainBlocked}
                 >
                   {testButtonLabel}
                 </Button>
@@ -1489,7 +1527,9 @@ export function MCP({ initialServerId }: MCPProps) {
                     Cancel
                   </Button>
                   <Button onClick={handleAddServer} disabled={isSubmitDisabled} variant='tertiary'>
-                    {isSubmitDisabled && isFormValid ? 'Adding...' : 'Add Server'}
+                    {isSubmitDisabled && isFormValid && !isAddDomainBlocked
+                      ? 'Adding...'
+                      : 'Add Server'}
                   </Button>
                 </div>
               </div>

apps/sim/ee/sso/components/sso-settings.tsx

@@ -2,7 +2,7 @@
 
 import { useState } from 'react'
 import { createLogger } from '@sim/logger'
-import { Check, ChevronDown, Copy, Eye, EyeOff } from 'lucide-react'
+import { Check, ChevronDown, Clipboard, Eye, EyeOff } from 'lucide-react'
 import { Button, Combobox, Input, Switch, Textarea } from '@/components/emcn'
 import { Skeleton } from '@/components/ui'
 import { useSession } from '@/lib/auth/auth-client'
@@ -418,29 +418,29 @@ export function SSO() {
 
             {/* Callback URL */}
             <div className='flex flex-col gap-[8px]'>
-              <span className='font-medium text-[13px] text-[var(--text-secondary)]'>
-                Callback URL
-              </span>
-              <div className='relative'>
-                <div className='flex h-9 items-center rounded-[6px] border bg-[var(--surface-1)] px-[10px] pr-[40px]'>
-                  <code className='flex-1 truncate font-mono text-[13px] text-[var(--text-primary)]'>
-                    {providerCallbackUrl}
-                  </code>
-                </div>
+              <div className='flex items-center justify-between'>
+                <span className='font-medium text-[13px] text-[var(--text-secondary)]'>
+                  Callback URL
+                </span>
                 <Button
                   type='button'
                   variant='ghost'
                   onClick={() => copyToClipboard(providerCallbackUrl)}
-                  className='-translate-y-1/2 absolute top-1/2 right-[4px] h-[28px] w-[28px] rounded-[4px] text-[var(--text-muted)] hover:text-[var(--text-primary)]'
+                  className='h-[22px] w-[22px] rounded-[4px] p-0 text-[var(--text-muted)] hover:text-[var(--text-primary)]'
                 >
                   {copied ? (
-                    <Check className='h-[14px] w-[14px]' />
+                    <Check className='h-[13px] w-[13px]' />
                   ) : (
-                    <Copy className='h-[14px] w-[14px]' />
+                    <Clipboard className='h-[13px] w-[13px]' />
                   )}
                   <span className='sr-only'>Copy callback URL</span>
                 </Button>
               </div>
+              <div className='flex h-9 items-center rounded-[6px] border bg-[var(--surface-1)] px-[10px]'>
+                <code className='flex-1 truncate font-mono text-[13px] text-[var(--text-primary)]'>
+                  {providerCallbackUrl}
+                </code>
+              </div>
               <p className='text-[13px] text-[var(--text-muted)]'>
                 Configure this in your identity provider
               </p>
@@ -852,29 +852,29 @@ export function SSO() {
 
           {/* Callback URL display */}
           <div className='flex flex-col gap-[8px]'>
-            <span className='font-medium text-[13px] text-[var(--text-secondary)]'>
-              Callback URL
-            </span>
-            <div className='relative'>
-              <div className='flex h-9 items-center rounded-[6px] border bg-[var(--surface-1)] px-[10px] pr-[40px]'>
-                <code className='flex-1 truncate font-mono text-[13px] text-[var(--text-primary)]'>
-                  {callbackUrl}
-                </code>
-              </div>
+            <div className='flex items-center justify-between'>
+              <span className='font-medium text-[13px] text-[var(--text-secondary)]'>
+                Callback URL
+              </span>
               <Button
                 type='button'
                 variant='ghost'
                 onClick={() => copyToClipboard(callbackUrl)}
-                className='-translate-y-1/2 absolute top-1/2 right-[4px] h-[28px] w-[28px] rounded-[4px] text-[var(--text-muted)] hover:text-[var(--text-primary)]'
+                className='h-[22px] w-[22px] rounded-[4px] p-0 text-[var(--text-muted)] hover:text-[var(--text-primary)]'
               >
                 {copied ? (
-                  <Check className='h-[14px] w-[14px]' />
+                  <Check className='h-[13px] w-[13px]' />
                 ) : (
-                  <Copy className='h-[14px] w-[14px]' />
+                  <Clipboard className='h-[13px] w-[13px]' />
                 )}
                 <span className='sr-only'>Copy callback URL</span>
               </Button>
             </div>
+            <div className='flex h-9 items-center rounded-[6px] border bg-[var(--surface-1)] px-[10px]'>
+              <code className='flex-1 truncate font-mono text-[13px] text-[var(--text-primary)]'>
+                {callbackUrl}
+              </code>
+            </div>
             <p className='text-[13px] text-[var(--text-muted)]'>
               Configure this in your identity provider
             </p>

apps/sim/lib/core/config/env.ts

@@ -93,6 +93,7 @@ export const env = createEnv({
     EXA_API_KEY:                           z.string().min(1).optional(),           // Exa AI API key for enhanced online search
     BLACKLISTED_PROVIDERS:                 z.string().optional(),                  // Comma-separated provider IDs to hide (e.g., "openai,anthropic")
     BLACKLISTED_MODELS:                    z.string().optional(),                  // Comma-separated model names/prefixes to hide (e.g., "gpt-4,claude-*")
+    ALLOWED_MCP_DOMAINS:                   z.string().optional(),                  // Comma-separated domains for MCP servers (e.g., "internal.company.com,mcp.example.org"). Empty = all allowed.
 
     // Azure Configuration - Shared credentials with feature-specific models
     AZURE_OPENAI_ENDPOINT:                 z.string().url().optional(),            // Shared Azure OpenAI service endpoint

apps/sim/lib/core/config/feature-flags.ts

@@ -123,6 +123,35 @@ export const isReactGrabEnabled = isDev && isTruthy(env.REACT_GRAB_ENABLED)
  */
 export const isReactScanEnabled = isDev && isTruthy(env.REACT_SCAN_ENABLED)
 
+/**
+ * Normalizes a domain entry from the ALLOWED_MCP_DOMAINS env var.
+ * Accepts bare hostnames (e.g., "mcp.company.com") or full URLs (e.g., "https://mcp.company.com").
+ * Extracts the hostname in either case.
+ */
+function normalizeDomainEntry(entry: string): string {
+  const trimmed = entry.trim().toLowerCase()
+  if (!trimmed) return ''
+  if (trimmed.includes('://')) {
+    try {
+      return new URL(trimmed).hostname
+    } catch {
+      return trimmed
+    }
+  }
+  return trimmed
+}
+
+/**
+ * Get allowed MCP server domains from the ALLOWED_MCP_DOMAINS env var.
+ * Returns null if not set (all domains allowed), or parsed array of lowercase hostnames.
+ * Accepts both bare hostnames and full URLs in the env var value.
+ */
+export function getAllowedMcpDomainsFromEnv(): string[] | null {
+  if (!env.ALLOWED_MCP_DOMAINS) return null
+  const parsed = env.ALLOWED_MCP_DOMAINS.split(',').map(normalizeDomainEntry).filter(Boolean)
+  return parsed.length > 0 ? parsed : null
+}
+
 /**
  * Get cost multiplier based on environment
  */