diff --git a/apps/api/app/api/routes/upload.py b/apps/api/app/api/routes/upload.py
index e0ee6fd4d..2e16d836b 100644
--- a/apps/api/app/api/routes/upload.py
+++ b/apps/api/app/api/routes/upload.py
@@ -25,6 +25,13 @@ from packages.ports.workspace_member_repository import WorkspaceMemberRepository
 
 router = APIRouter()
 
+# Allowed MIME types for file uploads (P2-5: Server-side validation)
+ALLOWED_MIME_TYPES = {
+    "image/jpeg", "image/png", "image/gif", "image/webp",
+    "video/mp4", "video/quicktime", "video/x-msvideo", "video/webm",
+    "audio/mpeg", "audio/wav", "audio/ogg", "audio/mp3",
+}
+
 
 def _require_workspace_member(
     workspace_id: str,
@@ -72,6 +79,37 @@ def _submit_ingest_job(
     return job
 
 
+def _validate_file_type(content: bytes, filename: str) -> str:
+    """
+    P2-5: Server-side file type validation using python-magic.
+    
+    Args:
+        content: File content bytes
+        filename: Original filename
+        
+    Returns:
+        Detected MIME type
+        
+    Raises:
+        HTTPException: If file type is not allowed
+    """
+    try:
+        import magic
+        detected_mime = magic.from_buffer(content, mime=True)
+    except ImportError:
+        # Fallback: infer from extension if magic is not available
+        import mimetypes
+        detected_mime = mimetypes.guess_type(filename)[0] or "application/octet-stream"
+    
+    if detected_mime not in ALLOWED_MIME_TYPES:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail=f"Unsupported file type: {detected_mime}. Allowed types: {', '.join(sorted(ALLOWED_MIME_TYPES))}"
+        )
+    
+    return detected_mime
+
+
 @router.post("/direct/prepare", response_model=DirectUploadPrepareResponse)
 async def prepare_direct_upload(
     request: DirectUploadPrepareRequest,
@@ -81,7 +119,7 @@ async def prepare_direct_upload(
     workspace_member_repository: WorkspaceMemberRepository = Depends(get_workspace_member_repository),
     storage_service: OSSStorageService = Depends(get_storage_service),
 ) -> DirectUploadPrepareResponse:
-    """创建浏览器直传 OSS 的短期表单签名。"""
+    """Prepare direct upload to OSS"""
     settings = get_settings()
     max_size_bytes = settings.OSS_DIRECT_UPLOAD_MAX_MB * 1024 * 1024
     if request.file_size > max_size_bytes:
@@ -132,7 +170,7 @@ async def complete_direct_upload(
     workspace_member_repository: WorkspaceMemberRepository = Depends(get_workspace_member_repository),
     storage_service: OSSStorageService = Depends(get_storage_service),
 ) -> DirectUploadCompleteResponse:
-    """确认浏览器直传完成并创建导入任务。"""
+    """Complete direct upload"""
     _require_workspace_member(request.workspace_id, authenticated_user, workspace_member_repository)
     _require_project_and_library(
         request.workspace_id,
@@ -159,10 +197,10 @@ async def complete_direct_upload(
 
 @router.post("", response_model=UploadAssetResponse)
 async def upload_asset(
-    file: UploadFile = File(..., description="要上传的文件（视频、音频、图片等）"),
+    file: UploadFile = File(..., description="文件上传"),
     workspace_id: str = Form(..., description="工作空间 ID"),
     project_id: str = Form(..., description="项目 ID"),
-    library_id: str = Form(..., description="素材库 ID"),
+    library_id: str = Form(..., description="资产库 ID"),
     authenticated_user: AuthenticatedUser = Depends(get_current_user),
     ingest_job_repository: Any = Depends(get_ingest_job_repository),
     project_repository: Any = Depends(get_project_repository),
@@ -170,17 +208,26 @@ async def upload_asset(
     workspace_member_repository: WorkspaceMemberRepository = Depends(get_workspace_member_repository),
     storage_service: OSSStorageService = Depends(get_storage_service),
 ) -> UploadAssetResponse:
-    """上传素材文件并触发导入流水线。"""
+    """Upload asset file"""
     _require_workspace_member(workspace_id, authenticated_user, workspace_member_repository)
     _require_project_and_library(workspace_id, project_id, library_id, project_repository, asset_library_repository)
 
+    # Read file content for validation (P2-5)
+    file_content = await file.read()
+    
+    # P2-5: Server-side file type validation
+    detected_mime = _validate_file_type(file_content, file.filename)
+    
+    # Reset file pointer for upload
+    await file.seek(0)
+    
     file_id = uuid4().hex[:8]
     storage_key = f"uploads/{file_id}/{file.filename}"
 
     file_url = storage_service.upload_file(
         file.file,
         storage_key,
-        content_type=file.content_type or "application/octet-stream",
+        content_type=file.content_type or detected_mime,
     )
 
     job = _submit_ingest_job(