GHSA-gq96-5pfx-f4vc

## Summary

The `/api/_action/media/external-link` endpoint allows authenticated admin users to make server-side HTTP HEAD requests to arbitrary internal IP addresses. While the parallel `uploadFromURL` flow validates target IPs against private/reserved ranges via `FileUrlValidator`, the `linkURL` flow only performs a URL format check (regex for `http://` or `https://` prefix), allowing SSRF to internal network services and cloud metadata endpoints.

## Details

The vulnerability is an inconsistency between two URL-handling flows in `MediaUploadService`.

**Vulnerable path** (`external-link`):

`MediaUploadV2Controller::externalLink()` at `src/Core/Content/Media/Api/MediaUploadV2Controller.php:66` takes a user-supplied `url` parameter and passes it to `MediaUploadService::linkURL()` at `src/Core/Content/Media/Upload/MediaUploadService.php:134`.

`linkURL()` calls `getContentSizeFromValidExternalUrl($url)` at line 159, which only validates via `validateExternalUrl()`:

```php // src/Core/Content/Media/Upload/MediaUploadService.php:207-212 public static function validateExternalUrl(string $url): void { if (!preg_match('/^https?:\/\/.+/', $url)) { throw MediaException::invalidUrl($url); } } ```

Then makes a server-side HEAD request with no IP filtering:

```php // src/Core/Content/Media/Upload/MediaUploadService.php:292-300 private function getContentSizeFromValidExternalUrl(string $url): int { $this->validateExternalUrl($url);

$headers = $this->httpClient->request('HEAD', $url)->getHeaders(); if (!\array_key_exists('content-length', $headers)) { throw MediaException::fileNotFound($url); }

return (int) $headers['content-length'][0]; } ```

**Protected path** (`upload_by_url`):

In contrast, `uploadFromURL` uses `FileFetcher::fetchFromURL()` which calls `FileUrlValidator::isValid()`:

```php // src/Core/Content/Media/File/FileFetcher.php:64 if ($this->enableUrlValidation && !$this->fileUrlValidator->isValid($url)) { throw MediaException::illegalUrl($url); } ```

`FileUrlValidator::isValid()` resolves the hostname via `gethostbyname()` and validates the IP against private and reserved ranges using `filter_var()` with `FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE`. This protection is entirely absent from the `linkURL` flow.

## Impact

An authenticated admin user can:

1. **Probe cloud metadata services** — HEAD requests to `169.254.169.254` reveal whether cloud metadata endpoints exist and leak content-length values 2. **Scan internal networks** — Differentiate open/closed/filtered ports on internal hosts (10.x, 172.16.x, 192.168.x) based on response timing and error types 3. **Leak internal service information** — The `fileSize` field stored in the database reflects the `content-length` header from internal services 4. **Redirect-based escalation** — Symfony HttpClient follows redirects by default (max_redirects=20), allowing an attacker-controlled external server to redirect the HEAD request to arbitrary internal destinations

Impact is limited to information disclosure via HEAD requests. The admin authentication requirement (PR:H) reduces exploitability, but in multi-tenant or compromised-credential scenarios this allows network reconnaissance from the server's perspective.

## Recommended Fix

Apply `FileUrlValidator` to the `linkURL` flow, consistent with the `uploadFromURL` flow. In `MediaUploadService`:

```php // src/Core/Content/Media/Upload/MediaUploadService.php

// Add constructor dependency: private readonly FileUrlValidatorInterface $fileUrlValidator;

// In getContentSizeFromValidExternalUrl(), add IP validation: private function getContentSizeFromValidExternalUrl(string $url): int { $this->validateExternalUrl($url);

if (!$this->fileUrlValidator->isValid($url)) { throw MediaException::illegalUrl($url); }

$headers = $this->httpClient->request('HEAD', $url)->getHeaders(); if (!\array_key_exists('content-length', $headers)) { throw MediaException::fileNotFound($url); }

return (int) $headers['content-length'][0]; } ```

Additionally, consider setting `max_redirects: 0` on the HttpClient request to prevent redirect-based SSRF bypasses.