NukeViet: Pre-authentication SSRF via X-Forwarded-Host

Summary

An unauthenticated attacker can coerce the server into issuing HTTP requests to an attacker-chosen host by spoofing the X Forwarded-Host (and X-Forwarded-Proto) request headers. The forwarded host is used, without validation, to build the URL that server_info_update() fetches with cURL, resulting in a Server-Side Request Forgery (SSRF) that requires no authentication.

Affected component

• File: includes/ini.php — function server_info_update() (cURL sink)
• File: vendor/vinades/nukeviet/Core/Server.php — standardizeHost() and the forwarded-header handling in the constructor (source of the tainted host)
• Trigger: POST request containing the field __serverInfoUpdate=1, handled early in includes/ini.php before any authentication.

Details

NukeViet\Core\Server derives original_host / original_protocol from the X-Forwarded-Host / X-Forwarded-Proto headers and exposes them via getOriginalHost() / getOriginalProtocol(). These values are attacker-controlled and were not validated against the site's configured domains (my_domains).

In server_info_update() the tainted host and scheme are concatenated directly into a cURL URL:

$proto = $nv_Server->getOriginalProtocol();   // from X-Forwarded-Proto
$host  = $nv_Server->getOriginalHost();        // from X-Forwarded-Host
$ch = curl_init($proto . '://' . $host . NV_BASE_SITEURL . 'index.php?response_headers_detect=1');
curl_exec($ch);

Two factors made this reliably reachable:

1. The __serverInfoUpdate handler runs very early in includes/ini.php, before authentication, so the sink is reachable pre-auth.
2. The host sanitiser standardizeHost() stripped a trailing port only with the regex (\:[0-9]+)$, which is bypassed by appending a slash (e.g. 127.0.0.1:8081/): the string no longer ends in :digits, so the port survives and an arbitrary host:port reaches the cURL call.

Proof of Concept

POST /index.php HTTP/1.1
Host: <victim>
X-Forwarded-Proto: http
X-Forwarded-Host: <attacker-controlled-host>:<port>/
Content-Type: application/x-www-form-urlencoded
Content-Length: 20

__serverInfoUpdate=1

The server then issues a request to the attacker-supplied host, confirmed via an out-of-band interaction (DNS + HTTP) on a collaborator endpoint.

Impact

The SSRF is blind, HEAD-only, and uses a fixed request path (…/index.php?response_headers_detect=1):

• The fetched response is stored server-side in the config_ini cache and is not reflected to the attacker, so internal data cannot be exfiltrated directly.
• Because the path is fixed and not attacker-controlled, cloud metadata endpoints (e.g. 169.254.169.254/latest/meta-data/...) cannot be reached, and gopher:// / dict:// request smuggling cannot inject arbitrary payloads.

What an attacker can do: unauthenticated internal host/port discovery (connection success/timing, with the port reachable through the regex bypass), and poisoning of the cached server_headers (the SSRF target's response headers are stored and applied to the site).

Severity

Rated High rather than Critical, because the blind + fixed-path + HEAD design of the sink prevents data exfiltration, cloud credential theft, and internal RCE.

• CVSS v3.1 Base Score: 7.2 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

Weakness

• Primary: CWE-918: Server-Side Request Forgery (SSRF)
• Contributing: CWE-20 (Improper Input Validation), CWE-644 (Improper Neutralization of HTTP Headers used by downstream components / trusting X-Forwarded-*).

Remediation

Fixed by validating and normalising the forwarded values at the source and gating the request before the sink:

• standardizeHost() now extracts the host with parse_url() (defeats the :port/ bypass) and lower-cases it.
• X-Forwarded-Proto is restricted to a {http, https} allow-list and falls back to the real server protocol otherwise.
• X-Forwarded-Port is validated as numeric and within range.
• The incoming host is checked against my_domains before includes/ini.php is reached; non-matching hosts are rejected/redirected, and server_info_update() additionally re-validates its target host against my_domains (defense in depth).

Workaround

Configure the reverse proxy / web server to strip or override client-supplied X-Forwarded-Host, X-Forwarded-Proto, and X-Forwarded-Port headers, and ensure my_domains is configured with the site's canonical domain(s).