fix(backend): validate the S3 endpoint host before the restore download

downloadFileFromS3() built an S3StorageAdapter and called .download()
directly, skipping the isHostAllowed() private-IP/DNS-rebinding guard
that testConnection() applies elsewhere — an admin with backup.restore
could point the configured S3 endpoint at an internal/metadata address
for unauthenticated egress via the server.

backend/__tests__/services/restoreServiceS3Ssrf.test.js

@@ -0,0 +1,109 @@
+/**
+ * Blind SSRF via the restore S3 download path (GHSA-vm2x-c628-3cx5).
+ *
+ * downloadFileFromS3() built a bare S3StorageAdapter and called .download()
+ * directly, never running the DNS-resolving isHostAllowed() guard that
+ * testConnection() applies elsewhere — so an admin with backup.restore could
+ * point the request-supplied S3 endpoint at an internal/metadata address for
+ * unauthenticated egress via the server. `s3Config` here is fully attacker
+ * controlled (POST /api/admin/restore/validate and /restore/start take it
+ * straight from the request body — see routes/adminRestore.js), unlike the
+ * scheduled-backup S3 endpoint, which is vetted at settings-save time.
+ */
+
+const path = require('path');
+const fs = require('fs');
+const os = require('os');
+
+process.env.NODE_ENV = 'test';
+process.env.TEST_DATABASE_PATH = path.join(
+  fs.mkdtempSync(path.join(os.tmpdir(), 'picpeak-restores3ssrf-')), 'db.sqlite',
+);
+process.env.JWT_SECRET = process.env.JWT_SECRET || 'restores3ssrf-test-secret';
+
+jest.mock('dns', () => {
+  const actual = jest.requireActual('dns');
+  return { ...actual, promises: { ...actual.promises, lookup: jest.fn() } };
+});
+
+jest.mock('../../src/services/storage/s3Storage', () =>
+  jest.fn().mockImplementation(() => ({
+    download: jest.fn().mockResolvedValue(undefined),
+  }))
+);
+
+const dns = require('dns');
+const lookup = dns.promises.lookup;
+const S3StorageAdapter = require('../../src/services/storage/s3Storage');
+const { RestoreService } = require('../../src/services/restoreService');
+
+describe('downloadFileFromS3 SSRF guard (GHSA-vm2x-c628-3cx5)', () => {
+  let restoreService;
+  let originalNodeEnv;
+
+  beforeEach(() => {
+    restoreService = new RestoreService();
+    lookup.mockReset();
+    S3StorageAdapter.mockClear();
+    originalNodeEnv = process.env.NODE_ENV;
+    process.env.NODE_ENV = 'production';
+  });
+
+  afterEach(() => {
+    process.env.NODE_ENV = originalNodeEnv;
+  });
+
+  it('rejects an endpoint hostname that resolves to a private/internal address before any network call', async () => {
+    lookup.mockResolvedValue([{ address: '10.0.0.5', family: 4 }]);
+
+    await expect(
+      restoreService.downloadFileFromS3(
+        's3://backups/manifest.json',
+        '/tmp/whatever/manifest.json',
+        { endpoint: 'evil-rebind.example.com', accessKeyId: 'k', secretAccessKey: 's' }
+      )
+    ).rejects.toThrow(/private or internal network address/i);
+
+    expect(S3StorageAdapter).not.toHaveBeenCalled();
+  });
+
+  it('rejects an endpoint hostname that resolves to the cloud metadata address', async () => {
+    lookup.mockResolvedValue([{ address: '169.254.169.254', family: 4 }]);
+
+    await expect(
+      restoreService.downloadFileFromS3(
+        's3://backups/manifest.json',
+        '/tmp/whatever/manifest.json',
+        { endpoint: 'metadata-rebind.example.com', accessKeyId: 'k', secretAccessKey: 's' }
+      )
+    ).rejects.toThrow(/private or internal network address/i);
+
+    expect(S3StorageAdapter).not.toHaveBeenCalled();
+  });
+
+  it('allows a legitimate public S3 endpoint through to download()', async () => {
+    lookup.mockResolvedValue([{ address: '93.184.216.34', family: 4 }]);
+
+    await restoreService.downloadFileFromS3(
+      's3://backups/manifest.json',
+      '/tmp/whatever/manifest.json',
+      { endpoint: 's3.example-cdn.com', accessKeyId: 'k', secretAccessKey: 's' }
+    );
+
+    expect(S3StorageAdapter).toHaveBeenCalledTimes(1);
+  });
+
+  it('does not require the guard outside production (dev MinIO stays usable), but still downloads', async () => {
+    process.env.NODE_ENV = 'development';
+    lookup.mockResolvedValue([{ address: '10.0.0.5', family: 4 }]); // would be rejected in prod
+
+    await restoreService.downloadFileFromS3(
+      's3://backups/manifest.json',
+      '/tmp/whatever/manifest.json',
+      { endpoint: 'localhost:9000', accessKeyId: 'k', secretAccessKey: 's' }
+    );
+
+    expect(lookup).not.toHaveBeenCalled();
+    expect(S3StorageAdapter).toHaveBeenCalledTimes(1);
+  });
+});

backend/src/services/restoreService.js

@@ -1628,6 +1628,23 @@ END $$;`
       throw new Error('Invalid S3 URL format');
     }
 
+    // SSRF guard: this method calls S3StorageAdapter.download() directly
+    // rather than going through testConnection(), so it must re-run the same
+    // DNS-resolving host check testConnection() applies — otherwise an
+    // admin-configured S3 endpoint could point at a private/internal or
+    // cloud-metadata address for unauthenticated egress via the server.
+    // Prod-only, matching S3StorageAdapter's own gate (dev points at
+    // localhost MinIO deliberately).
+    if (process.env.NODE_ENV === 'production' && s3Config && s3Config.endpoint) {
+      const { isHostAllowed } = require('../utils/networkValidation');
+      const { hostname } = new URL(
+        /^https?:\/\//.test(s3Config.endpoint) ? s3Config.endpoint : `https://${s3Config.endpoint}`
+      );
+      if (!(await isHostAllowed(hostname))) {
+        throw new Error('S3 endpoint resolves to a private or internal network address');
+      }
+    }
+
     const [, bucket, key] = s3PathMatch;
     const s3Client = new S3StorageAdapter({
       ...s3Config,