[9.0] [Fleet] Improve file content type validation (elastic#234551) (elastic#234857)

# Backport

This will backport the following commits from `main` to `9.0`:
- [[Fleet] Improve file content type validation
(elastic#234551)](elastic#234551)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT [{"author":{"name":"Nicolas
Chaulet","email":"[email protected]"},"sourceCommit":{"committedDate":"2025-09-12T06:54:00Z","message":"[Fleet]
Improve file content type validation
(elastic#234551)","sha":"0c5ab7ec467579bbe9c1feb5007efa811487db11","branchLabelMapping":{"^v9.2.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:skip","Team:Fleet","backport:all-open","v9.2.0"],"title":"[Fleet]
Improve file content type
validation","number":234551,"url":"https://github.com/elastic/kibana/pull/234551","mergeCommit":{"message":"[Fleet]
Improve file content type validation
(elastic#234551)","sha":"0c5ab7ec467579bbe9c1feb5007efa811487db11"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.2.0","branchLabelMappingKey":"^v9.2.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/234551","number":234551,"mergeCommit":{"message":"[Fleet]
Improve file content type validation
(elastic#234551)","sha":"0c5ab7ec467579bbe9c1feb5007efa811487db11"}}]}]
BACKPORT-->

Co-authored-by: Nicolas Chaulet <[email protected]>

Author: kibanamachine

x-pack/platform/plugins/shared/fleet/server/routes/epm/file_handler.test.ts

@@ -96,6 +96,31 @@ describe('getFileHandler', () => {
     );
   });
 
+  it('should throw if the file is not supported for bundled package and an existing file', async () => {
+    mockedGetBundledPackageByPkgKey.mockResolvedValue({
+      getBuffer: () => Promise.resolve(),
+    } as any);
+    const request = httpServerMock.createKibanaRequest({
+      params: {
+        pkgName: 'test',
+        pkgVersion: '1.0.0',
+        filePath: 'test.zip',
+      },
+    });
+    const buffer = Buffer.from(`TEST`);
+    mockedUnpackBufferEntries.mockResolvedValue([
+      {
+        path: 'test-1.0.0/test.zip',
+        buffer,
+      },
+    ]);
+    const response = httpServerMock.createResponseFactory();
+    const context = mockContext();
+    await expect(getFileHandler(context, request, response)).rejects.toThrow(
+      /File content type "application\/zip" is not allowed to be retrieved/
+    );
+  });
+
   it('should a 404 for bundled package with a non existing file', async () => {
     mockedGetBundledPackageByPkgKey.mockResolvedValue({
       getBuffer: () => Promise.resolve(),
@@ -176,7 +201,7 @@ describe('getFileHandler', () => {
       body: 'not found',
       headers: new Headers({
         raw: '',
-        'content-type': 'text',
+        'content-type': 'text/plain',
       }),
     });
 
@@ -187,7 +212,7 @@ describe('getFileHandler', () => {
         statusCode: 404,
         body: 'not found',
         headers: expect.objectContaining({
-          'content-type': 'text',
+          'content-type': 'text/plain',
         }),
       })
     );
@@ -227,6 +252,33 @@ describe('getFileHandler', () => {
     );
   });
 
+  it('should throw if the file is not a supported extension for installed package', async () => {
+    const request = httpServerMock.createKibanaRequest({
+      params: {
+        pkgName: 'test',
+        pkgVersion: '1.0.0',
+        filePath: 'test.zip',
+      },
+    });
+    const response = httpServerMock.createResponseFactory();
+    const context = mockContext();
+
+    mockedGetInstallation.mockResolvedValue({ version: '1.0.0' } as any);
+    mockedGetAsset.mockResolvedValue({
+      asset_path: '/test/1.0.0/test.zip',
+      data_utf8: 'test',
+      data_base64: '',
+      media_type: 'application/zip',
+      package_name: 'test',
+      package_version: '1.0.0',
+      install_source: 'registry',
+    });
+
+    await expect(getFileHandler(context, request, response)).rejects.toThrow(
+      /File content type "application\/zip" is not allowed to be retrieved/
+    );
+  });
+
   it('should a 404 if the file from installation do not exists for installed package', async () => {
     const request = httpServerMock.createKibanaRequest({
       params: {

x-pack/platform/plugins/shared/fleet/server/routes/epm/file_handler.ts

@@ -17,10 +17,30 @@ import { getAsset } from '../../services/epm/archive/storage';
 import { getBundledPackageByPkgKey } from '../../services/epm/packages/bundled_packages';
 import { pkgToPkgKey } from '../../services/epm/registry';
 import { unpackArchiveEntriesIntoMemory } from '../../services/epm/archive';
+import { FleetError } from '../../errors';
 
 const CACHE_CONTROL_10_MINUTES_HEADER: HttpResponseOptions['headers'] = {
   'cache-control': 'max-age=600',
 };
+
+const ALLOWED_MIME_TYPES = [
+  'image/svg+xml',
+  'image/jpeg',
+  'image/png',
+  'image/gif',
+  'application/json',
+  'application/yaml',
+  'text/plain',
+  'text/markdown',
+  'text/yaml',
+];
+
+function validateContentTypeIsAllowed(contentType: string) {
+  if (!ALLOWED_MIME_TYPES.includes(contentType.split(';')[0])) {
+    throw new FleetError(`File content type "${contentType}" is not allowed to be retrieved`, 400);
+  }
+}
+
 export const getFileHandler: FleetRequestHandler<
   TypeOf<typeof GetFileRequestSchema.params>
 > = async (context, request, response) => {
@@ -42,6 +62,7 @@ export const getFileHandler: FleetRequestHandler<
     }
 
     const contentType = storedAsset.media_type;
+    validateContentTypeIsAllowed(contentType);
     const buffer = storedAsset.data_utf8
       ? Buffer.from(storedAsset.data_utf8, 'utf8')
       : Buffer.from(storedAsset.data_base64, 'base64');
@@ -94,6 +115,7 @@ export const getFileHandler: FleetRequestHandler<
         statusCode: 400,
       });
     }
+    validateContentTypeIsAllowed(contentType);
 
     return response.custom({
       body: buffer,
@@ -121,6 +143,11 @@ export const getFileHandler: FleetRequestHandler<
       return headers;
     }, {} as ResponseHeaders);
 
+    if (!proxiedHeaders['content-type'] || typeof proxiedHeaders['content-type'] !== 'string') {
+      throw new FleetError(`unknown content type for file: ${filePath}`);
+    }
+    validateContentTypeIsAllowed(proxiedHeaders['content-type']);
+
     return response.custom({
       body: registryResponse.body,
       statusCode: registryResponse.status,

x-pack/platform/plugins/shared/fleet/server/routes/epm/handlers.ts

@@ -578,6 +578,7 @@ export const getInputsHandler: FleetRequestHandler<
       prerelease,
       ignoreUnverified
     );
+    return response.ok({ body });
   } else if (format === 'yml' || format === 'yaml') {
     body = await getTemplateInputs(
       soClient,
@@ -587,8 +588,10 @@ export const getInputsHandler: FleetRequestHandler<
       prerelease,
       ignoreUnverified
     );
+
+    return response.ok({ body, headers: { 'content-type': 'text/yaml;charset=utf-8' } });
   }
-  return response.ok({ body });
+  throw new FleetError(`Fleet error template format not supported ${format}`);
 };
 
 // Don't expose the whole SO in the API response, only selected fields