Merge pull request #13054 from backstage/rugvip/safechild

backend-common: validate zip archive paths when unpacking into a dir

.changeset/dirty-pears-allow.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-common': patch
+---
+
+Added a second validation to the `dir()` method of ZIP archive responses returned from `readTree()` that ensures that extracted files do not fall outside the target directory.

packages/backend-common/src/reading/tree/ZipArchiveResponse.test.ts

@@ -28,6 +28,9 @@ const archiveDataCorrupted = fs.readFileSync(
 const archiveDataWithExtraDir = fs.readFileSync(
   resolvePath(__filename, '../../__fixtures__/mock-with-extra-root-dir.zip'),
 );
+const archiveWithMaliciousEntry = fs.readFileSync(
+  resolvePath(__filename, '../../__fixtures__/mallory.zip'),
+);
 
 describe('ZipArchiveResponse', () => {
   beforeEach(() => {
@@ -35,6 +38,7 @@ describe('ZipArchiveResponse', () => {
       '/test-archive.zip': archiveData,
       '/test-archive-with-extra-root-dir.zip': archiveDataWithExtraDir,
       '/test-archive-corrupted.zip': archiveDataCorrupted,
+      '/test-archive-malicious.zip': archiveWithMaliciousEntry,
       '/tmp': mockFs.directory(),
     });
   });
@@ -167,4 +171,22 @@ describe('ZipArchiveResponse', () => {
       'invalid comment length. expected: 55. found: 0',
     );
   });
+
+  it('should throw on entries with a path outside the destination dir', async () => {
+    const stream = fs.createReadStream('/test-archive-malicious.zip');
+
+    const res = new ZipArchiveResponse(stream, '', '/tmp', 'etag');
+    await expect(res.files()).rejects.toThrow(
+      'invalid relative path: ../side.txt',
+    );
+  });
+
+  it('should throw on entries that attempt to write outside destination dir', async () => {
+    const stream = fs.createReadStream('/test-archive-malicious.zip');
+
+    const res = new ZipArchiveResponse(stream, '', '/tmp', 'etag');
+    await expect(res.dir()).rejects.toThrow(
+      'invalid relative path: ../side.txt',
+    );
+  });
 });

packages/backend-common/src/reading/tree/ZipArchiveResponse.ts

@@ -25,6 +25,7 @@ import {
   ReadTreeResponseFile,
 } from '../types';
 import { streamToBuffer } from './util';
+import { resolveSafeChildPath } from '../../paths';
 
 /**
  * Wraps a zip archive stream into a tree response reader.
@@ -187,10 +188,10 @@ export class ZipArchiveResponse implements ReadTreeResponse {
       const dirname = platformPath.dirname(entryPath);
 
       if (dirname) {
-        await fs.mkdirp(platformPath.join(dir, dirname));
+        await fs.mkdirp(resolveSafeChildPath(dir, dirname));
       }
       return new Promise(async (resolve, reject) => {
-        const file = fs.createWriteStream(platformPath.join(dir, entryPath));
+        const file = fs.createWriteStream(resolveSafeChildPath(dir, entryPath));
         file.on('finish', resolve);
 
         content.on('error', reject);