Serendipity has a Host Header Injection allows authentication cookie scoping to attacker-controlled domain in functions_config.inc.php
Summary
The serendipity_setCookie() function uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker can force authentication cookies — including session tokens and auto-login tokens — to be scoped to an attacker-controlled domain, facilitating session hijacking.
Details
In include/functions_config.inc.php:726:
```php
function serendipity_setCookie($name, $value, $securebyprot = true, ...) {
$host = $_SERVER['HTTP_HOST']; // ← attacker-controlled, no validation
if ($securebyprot) {
if ($pos = strpos($host, ":")) {
$host = substr($host, 0, $pos); // strips port only
}
}
setcookie("serendipity[$name]", $value, [
'domain' => $host, // ← poisoned domain
'httponly' => $httpOnly,
'samesite' => 'Strict'
]);
}
```
This function is called during login with sensitive cookies:
```php
// functions_config.inc.php:455-498
serendipity_setCookie('author_autologintoken', $rnd, true, false, true);
serendipity_setCookie('author_username', $user);
serendipity_setCookie('author_token', $hash);
```
If an attacker can influence the Host header at login time (e.g. via MITM, reverse proxy misconfiguration, or load balancer), authentication cookies are issued scoped to the attacker's domain instead of the legitimate one.
PoC
```bash
curl -v -X POST \
-H "Host: attacker.com" \
-d "serendipity[user]=admin&serendipity[pass]=admin" \
http://[TARGET]/serendipity_admin.php 2>&1 | grep -i "set-cookie"
```
Expected output:
```http
Set-Cookie: serendipity[author_token]=; domain=attacker.com; HttpOnly
```
Impact
- Session fixation — attacker pre-sets a cookie scoped to their domain, then tricks the victim into authenticating, inheriting the poisoned token
- Token leakage —
author_autologintoken scoped to wrong domain may be sent to attacker-controlled infrastructure - Privilege escalation — if admin logs in under a poisoned Host header, their admin token is compromised
Suggested Fix
Validate HTTP_HOST against the configured $serendipity['url'] before use:
```php
function serendipity_setCookie($name, $value, ...) {
global $serendipity;
$configured = parse_url($serendipity['url'], PHP_URL_HOST);
$host = preg_replace('/:[0-9]+$/', '', $_SERVER['HTTP_HOST']);
$host = ($host === $configured) ? $host : $configured;
setcookie("serendipity[$name]", $value, [
'domain' => $host,
...
]);
}
```
