Shopware: SSRF in Media External-Link Endpoint Bypasses IP Validation

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():

// 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:

// 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():

// 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:

// 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.