diff --git a/apps/sim/app/api/files/presigned/route.test.ts b/apps/sim/app/api/files/presigned/route.test.ts
index 6ae6a10ed5..7c4893dc44 100644
--- a/apps/sim/app/api/files/presigned/route.test.ts
+++ b/apps/sim/app/api/files/presigned/route.test.ts
@@ -17,10 +17,14 @@ const {
   mockIsUsingCloudStorage,
   mockGetStorageProvider,
   mockValidateFileType,
+  mockValidateAttachmentFileType,
   mockGenerateCopilotUploadUrl,
   mockIsImageFileType,
   mockGetStorageProviderUploads,
   mockIsUsingCloudStorageUploads,
+  mockGetUserEntityPermissions,
+  mockGenerateWorkspaceFileKey,
+  mockGenerateExecutionFileKey,
 } = vi.hoisted(() => ({
   mockVerifyFileAccess: vi.fn().mockResolvedValue(true),
   mockVerifyWorkspaceFileAccess: vi.fn().mockResolvedValue(true),
@@ -30,6 +34,7 @@ const {
   mockIsUsingCloudStorage: vi.fn(),
   mockGetStorageProvider: vi.fn(),
   mockValidateFileType: vi.fn().mockReturnValue(null),
+  mockValidateAttachmentFileType: vi.fn().mockReturnValue(null),
   mockGenerateCopilotUploadUrl: vi.fn().mockResolvedValue({
     url: 'https://example.com/presigned-url',
     key: 'copilot/test-key.txt',
@@ -37,6 +42,14 @@ const {
   mockIsImageFileType: vi.fn().mockReturnValue(true),
   mockGetStorageProviderUploads: vi.fn(),
   mockIsUsingCloudStorageUploads: vi.fn(),
+  mockGetUserEntityPermissions: vi.fn().mockResolvedValue('admin'),
+  mockGenerateWorkspaceFileKey: vi.fn(
+    (workspaceId: string, fileName: string) => `workspace/${workspaceId}/${fileName}`
+  ),
+  mockGenerateExecutionFileKey: vi.fn(
+    (ctx: { workspaceId: string; workflowId: string; executionId: string }, fileName: string) =>
+      `execution/${ctx.workspaceId}/${ctx.workflowId}/${ctx.executionId}/${fileName}`
+  ),
 }))
 
 vi.mock('@/app/api/files/authorization', () => ({
@@ -61,6 +74,19 @@ vi.mock('@/lib/uploads/core/storage-service', () => storageServiceMock)
 
 vi.mock('@/lib/uploads/utils/validation', () => ({
   validateFileType: mockValidateFileType,
+  validateAttachmentFileType: mockValidateAttachmentFileType,
+}))
+
+vi.mock('@/lib/workspaces/permissions/utils', () => ({
+  getUserEntityPermissions: mockGetUserEntityPermissions,
+}))
+
+vi.mock('@/lib/uploads/contexts/workspace/workspace-file-manager', () => ({
+  generateWorkspaceFileKey: mockGenerateWorkspaceFileKey,
+}))
+
+vi.mock('@/lib/uploads/contexts/execution/utils', () => ({
+  generateExecutionFileKey: mockGenerateExecutionFileKey,
 }))
 
 vi.mock('@/lib/uploads/utils/file-utils', () => ({
@@ -139,6 +165,8 @@ function setupFileApiMocks(
   )
 
   mockValidateFileType.mockReturnValue(null)
+  mockValidateAttachmentFileType.mockReturnValue(null)
+  mockGetUserEntityPermissions.mockResolvedValue('admin')
 
   mockGetStorageProviderUploads.mockReturnValue(
     storageProvider === 'blob' ? 'Azure Blob' : storageProvider === 's3' ? 'S3' : 'Local'
@@ -518,6 +546,167 @@ describe('/api/files/presigned', () => {
     })
   })
 
+  describe('mothership uploads', () => {
+    it('uses validateAttachmentFileType (not validateFileType) — accepts images', async () => {
+      setupFileApiMocks({ cloudEnabled: true, storageProvider: 's3' })
+
+      const request = new NextRequest(
+        'http://localhost:3000/api/files/presigned?type=mothership&workspaceId=ws-1',
+        {
+          method: 'POST',
+          body: JSON.stringify({
+            fileName: 'screenshot.png',
+            contentType: 'image/png',
+            fileSize: 4096,
+          }),
+        }
+      )
+
+      const response = await POST(request)
+      expect(response.status).toBe(200)
+      expect(mockValidateAttachmentFileType).toHaveBeenCalledWith('screenshot.png')
+      expect(mockValidateFileType).not.toHaveBeenCalled()
+    })
+
+    it('rejects unsupported types when validator returns an error', async () => {
+      setupFileApiMocks({ cloudEnabled: true, storageProvider: 's3' })
+      mockValidateAttachmentFileType.mockReturnValue({
+        code: 'UNSUPPORTED_FILE_TYPE',
+        message: 'Unsupported file type: exe.',
+        supportedTypes: [],
+      })
+
+      const request = new NextRequest(
+        'http://localhost:3000/api/files/presigned?type=mothership&workspaceId=ws-1',
+        {
+          method: 'POST',
+          body: JSON.stringify({
+            fileName: 'virus.exe',
+            contentType: 'application/octet-stream',
+            fileSize: 4096,
+          }),
+        }
+      )
+
+      const response = await POST(request)
+      const data = await response.json()
+      expect(response.status).toBe(400)
+      expect(data.code).toBe('VALIDATION_ERROR')
+      expect(data.error).toContain('exe')
+    })
+
+    it('returns 403 when user lacks workspace write permission', async () => {
+      setupFileApiMocks({ cloudEnabled: true, storageProvider: 's3' })
+      mockGetUserEntityPermissions.mockResolvedValue('read')
+
+      const request = new NextRequest(
+        'http://localhost:3000/api/files/presigned?type=mothership&workspaceId=ws-1',
+        {
+          method: 'POST',
+          body: JSON.stringify({
+            fileName: 'doc.pdf',
+            contentType: 'application/pdf',
+            fileSize: 4096,
+          }),
+        }
+      )
+
+      const response = await POST(request)
+      expect(response.status).toBe(403)
+    })
+  })
+
+  describe('execution uploads', () => {
+    it('uses validateAttachmentFileType — accepts video', async () => {
+      setupFileApiMocks({ cloudEnabled: true, storageProvider: 's3' })
+
+      const request = new NextRequest(
+        'http://localhost:3000/api/files/presigned?type=execution&workspaceId=ws-1&workflowId=wf-1&executionId=exec-1',
+        {
+          method: 'POST',
+          body: JSON.stringify({
+            fileName: 'output.mp4',
+            contentType: 'video/mp4',
+            fileSize: 4096,
+          }),
+        }
+      )
+
+      const response = await POST(request)
+      expect(response.status).toBe(200)
+      expect(mockValidateAttachmentFileType).toHaveBeenCalledWith('output.mp4')
+      expect(mockValidateFileType).not.toHaveBeenCalled()
+    })
+
+    it('rejects when validator returns an error', async () => {
+      setupFileApiMocks({ cloudEnabled: true, storageProvider: 's3' })
+      mockValidateAttachmentFileType.mockReturnValue({
+        code: 'UNSUPPORTED_FILE_TYPE',
+        message: 'Unsupported file type: bin.',
+        supportedTypes: [],
+      })
+
+      const request = new NextRequest(
+        'http://localhost:3000/api/files/presigned?type=execution&workspaceId=ws-1&workflowId=wf-1&executionId=exec-1',
+        {
+          method: 'POST',
+          body: JSON.stringify({
+            fileName: 'blob.bin',
+            contentType: 'application/octet-stream',
+            fileSize: 4096,
+          }),
+        }
+      )
+
+      const response = await POST(request)
+      const data = await response.json()
+      expect(response.status).toBe(400)
+      expect(data.code).toBe('VALIDATION_ERROR')
+    })
+
+    it('returns 400 when missing workflowId/executionId', async () => {
+      setupFileApiMocks({ cloudEnabled: true, storageProvider: 's3' })
+
+      const request = new NextRequest(
+        'http://localhost:3000/api/files/presigned?type=execution&workspaceId=ws-1',
+        {
+          method: 'POST',
+          body: JSON.stringify({
+            fileName: 'output.mp4',
+            contentType: 'video/mp4',
+            fileSize: 4096,
+          }),
+        }
+      )
+
+      const response = await POST(request)
+      expect(response.status).toBe(400)
+    })
+  })
+
+  describe('knowledge-base uploads', () => {
+    it('uses validateFileType (docs-only), not validateAttachmentFileType', async () => {
+      setupFileApiMocks({ cloudEnabled: true, storageProvider: 's3' })
+
+      const request = new NextRequest(
+        'http://localhost:3000/api/files/presigned?type=knowledge-base',
+        {
+          method: 'POST',
+          body: JSON.stringify({
+            fileName: 'doc.pdf',
+            contentType: 'application/pdf',
+            fileSize: 4096,
+          }),
+        }
+      )
+
+      const response = await POST(request)
+      expect(response.status).toBe(200)
+      expect(mockValidateFileType).toHaveBeenCalledWith('doc.pdf', 'application/pdf')
+      expect(mockValidateAttachmentFileType).not.toHaveBeenCalled()
+    })
+  })
+
   describe('OPTIONS', () => {
     it('should handle CORS preflight requests', async () => {
       const response = await OPTIONS()
diff --git a/apps/sim/app/api/files/presigned/route.ts b/apps/sim/app/api/files/presigned/route.ts
index c8fb824b3c..7c4bb01ec6 100644
--- a/apps/sim/app/api/files/presigned/route.ts
+++ b/apps/sim/app/api/files/presigned/route.ts
@@ -11,7 +11,7 @@ import { generateExecutionFileKey } from '@/lib/uploads/contexts/execution/utils
 import { generateWorkspaceFileKey } from '@/lib/uploads/contexts/workspace/workspace-file-manager'
 import { generatePresignedUploadUrl, hasCloudStorage } from '@/lib/uploads/core/storage-service'
 import { isImageFileType } from '@/lib/uploads/utils/file-utils'
-import { validateFileType } from '@/lib/uploads/utils/validation'
+import { validateAttachmentFileType, validateFileType } from '@/lib/uploads/utils/validation'
 import { getUserEntityPermissions } from '@/lib/workspaces/permissions/utils'
 import { createErrorResponse } from '@/app/api/files/utils'
 
@@ -141,7 +141,7 @@ export const POST = withRouteHandler(async (request: NextRequest) => {
         )
       }
 
-      const fileValidationError = validateFileType(fileName, contentType)
+      const fileValidationError = validateAttachmentFileType(fileName)
       if (fileValidationError) {
         throw new ValidationError(fileValidationError.message)
       }
@@ -175,7 +175,7 @@ export const POST = withRouteHandler(async (request: NextRequest) => {
         )
       }
 
-      const fileValidationError = validateFileType(fileName, contentType)
+      const fileValidationError = validateAttachmentFileType(fileName)
       if (fileValidationError) {
         throw new ValidationError(fileValidationError.message)
       }
diff --git a/apps/sim/app/api/files/upload/route.ts b/apps/sim/app/api/files/upload/route.ts
index 424935f594..828cf83aa0 100644
--- a/apps/sim/app/api/files/upload/route.ts
+++ b/apps/sim/app/api/files/upload/route.ts
@@ -15,11 +15,8 @@ import type { StorageContext } from '@/lib/uploads/config'
 import { generateWorkspaceFileKey } from '@/lib/uploads/contexts/workspace/workspace-file-manager'
 import { isImageFileType, resolveFileType } from '@/lib/uploads/utils/file-utils'
 import {
-  SUPPORTED_AUDIO_EXTENSIONS,
-  SUPPORTED_CODE_EXTENSIONS,
-  SUPPORTED_DOCUMENT_EXTENSIONS,
+  SUPPORTED_ATTACHMENT_EXTENSIONS,
   SUPPORTED_IMAGE_EXTENSIONS,
-  SUPPORTED_VIDEO_EXTENSIONS,
   validateFileType,
 } from '@/lib/uploads/utils/validation'
 import { getUserEntityPermissions } from '@/lib/workspaces/permissions/utils'
@@ -29,13 +26,7 @@ import {
   InvalidRequestError,
 } from '@/app/api/files/utils'
 
-const ALLOWED_EXTENSIONS = new Set<string>([
-  ...SUPPORTED_DOCUMENT_EXTENSIONS,
-  ...SUPPORTED_CODE_EXTENSIONS,
-  ...SUPPORTED_IMAGE_EXTENSIONS,
-  ...SUPPORTED_AUDIO_EXTENSIONS,
-  ...SUPPORTED_VIDEO_EXTENSIONS,
-])
+const ALLOWED_EXTENSIONS = new Set<string>(SUPPORTED_ATTACHMENT_EXTENSIONS)
 
 function validateFileExtension(filename: string): boolean {
   const extension = filename.split('.').pop()?.toLowerCase()
diff --git a/apps/sim/lib/uploads/utils/validation.test.ts b/apps/sim/lib/uploads/utils/validation.test.ts
new file mode 100644
index 0000000000..f5db99cbd0
--- /dev/null
+++ b/apps/sim/lib/uploads/utils/validation.test.ts
@@ -0,0 +1,73 @@
+import { describe, expect, it } from 'vitest'
+import {
+  SUPPORTED_ATTACHMENT_EXTENSIONS,
+  validateAttachmentFileType,
+} from '@/lib/uploads/utils/validation'
+
+describe('validateAttachmentFileType', () => {
+  it('accepts image files (png, jpg, gif, webp, svg)', () => {
+    expect(validateAttachmentFileType('screenshot.png')).toBeNull()
+    expect(validateAttachmentFileType('photo.jpg')).toBeNull()
+    expect(validateAttachmentFileType('photo.JPEG')).toBeNull()
+    expect(validateAttachmentFileType('animation.gif')).toBeNull()
+    expect(validateAttachmentFileType('image.webp')).toBeNull()
+    expect(validateAttachmentFileType('icon.svg')).toBeNull()
+  })
+
+  it('accepts video files (mp4, mov, webm)', () => {
+    expect(validateAttachmentFileType('clip.mp4')).toBeNull()
+    expect(validateAttachmentFileType('clip.mov')).toBeNull()
+    expect(validateAttachmentFileType('clip.webm')).toBeNull()
+  })
+
+  it('accepts audio files (mp3, wav, m4a)', () => {
+    expect(validateAttachmentFileType('voice.mp3')).toBeNull()
+    expect(validateAttachmentFileType('voice.wav')).toBeNull()
+    expect(validateAttachmentFileType('voice.m4a')).toBeNull()
+  })
+
+  it('accepts document files (pdf, docx, csv, md)', () => {
+    expect(validateAttachmentFileType('report.pdf')).toBeNull()
+    expect(validateAttachmentFileType('letter.docx')).toBeNull()
+    expect(validateAttachmentFileType('data.csv')).toBeNull()
+    expect(validateAttachmentFileType('notes.md')).toBeNull()
+  })
+
+  it('accepts code files (ts, py, sh, json)', () => {
+    expect(validateAttachmentFileType('app.ts')).toBeNull()
+    expect(validateAttachmentFileType('main.py')).toBeNull()
+    expect(validateAttachmentFileType('script.sh')).toBeNull()
+    expect(validateAttachmentFileType('config.json')).toBeNull()
+  })
+
+  it('rejects executables and unknown extensions', () => {
+    expect(validateAttachmentFileType('virus.exe')?.code).toBe('UNSUPPORTED_FILE_TYPE')
+    expect(validateAttachmentFileType('installer.msi')?.code).toBe('UNSUPPORTED_FILE_TYPE')
+    expect(validateAttachmentFileType('archive.dmg')?.code).toBe('UNSUPPORTED_FILE_TYPE')
+    expect(validateAttachmentFileType('binary.bin')?.code).toBe('UNSUPPORTED_FILE_TYPE')
+  })
+
+  it('rejects files with no extension', () => {
+    const result = validateAttachmentFileType('README')
+    expect(result?.code).toBe('UNSUPPORTED_FILE_TYPE')
+    expect(result?.message).toContain('README')
+  })
+
+  it('rejects files with non-alphanumeric extensions', () => {
+    expect(validateAttachmentFileType('odd.<>')?.code).toBe('UNSUPPORTED_FILE_TYPE')
+    expect(validateAttachmentFileType('foo. ')?.code).toBe('UNSUPPORTED_FILE_TYPE')
+  })
+
+  it('does not contain duplicate extensions (e.g. webm)', () => {
+    const seen = new Set<string>()
+    for (const ext of SUPPORTED_ATTACHMENT_EXTENSIONS) {
+      expect(seen.has(ext)).toBe(false)
+      seen.add(ext)
+    }
+  })
+
+  it('returns supportedTypes list in error', () => {
+    const result = validateAttachmentFileType('foo.exe')
+    expect(result?.supportedTypes).toEqual(expect.arrayContaining(['png', 'pdf', 'mp4', 'mp3']))
+  })
+})
diff --git a/apps/sim/lib/uploads/utils/validation.ts b/apps/sim/lib/uploads/utils/validation.ts
index af0a5581fb..4f46d67516 100644
--- a/apps/sim/lib/uploads/utils/validation.ts
+++ b/apps/sim/lib/uploads/utils/validation.ts
@@ -219,6 +219,37 @@ export interface FileValidationError {
   supportedTypes: string[]
 }
 
+export const SUPPORTED_ATTACHMENT_EXTENSIONS = Array.from(
+  new Set<string>([
+    ...SUPPORTED_DOCUMENT_EXTENSIONS,
+    ...SUPPORTED_CODE_EXTENSIONS,
+    ...SUPPORTED_IMAGE_EXTENSIONS,
+    ...SUPPORTED_AUDIO_EXTENSIONS,
+    ...SUPPORTED_VIDEO_EXTENSIONS,
+  ])
+) as readonly string[]
+
+/**
+ * Validate that a file's extension is allowed as a chat/mothership attachment.
+ *
+ * Permits documents, code, images, audio, and video — anything users would
+ * reasonably attach to a chat message. Rejects executables and unknown types.
+ */
+export function validateAttachmentFileType(fileName: string): FileValidationError | null {
+  const raw = extractExtension(fileName)
+  const extension = isAlphanumericExtension(raw) ? raw : ''
+
+  if (!SUPPORTED_ATTACHMENT_EXTENSIONS.includes(extension)) {
+    return {
+      code: 'UNSUPPORTED_FILE_TYPE',
+      message: `Unsupported file type${extension ? `: ${extension}` : ` for "${fileName}"`}. Supported types include documents, code, images, audio, and video.`,
+      supportedTypes: [...SUPPORTED_ATTACHMENT_EXTENSIONS],
+    }
+  }
+
+  return null
+}
+
 /**
  * Validate if a file type is supported for document processing
  */