Overview
In CVE-2017-9303, Laravel 5.4.x before 5.4.22 did not constrain the host portion of a password reset URL. This allowed an attacker to influence the host used in reset emails, making it easier to direct victims to attacker-controlled domains and harvest credentials through phishing. This class of vulnerability falls under CWE-20: Improper Input Validation. The risk is largely rooted in generating absolute URLs for password resets based on untrusted input, which can mislead users when they click a reset link mailed by the application.
An attacker could exploit this by triggering a password reset on a compromised or misconfigured Laravel instance and ensuring the generated reset link uses a host controlled by the attacker. Since password reset flows are typically initiated via user email, the victim might be directed to a look-alike domain, increasing the likelihood of credential theft. The vulnerability is mitigated once the host in the password reset URL is derived from a trusted source (e.g., the app's canonical URL) rather than the incoming request host.
Remediation focuses on ensuring that Laravel generates absolute URLs for password resets using the configured application URL, not the request host. Upgrading to a patched Laravel release (5.4.22 or newer) is essential, and you should also enforce a trusted root URL (APP_URL) for URL generation in your codebase. Additionally, review all code paths that construct absolute URLs from user input and add tests to verify that reset links always point to the canonical domain.
Affected Versions
Laravel 5.4.x before 5.4.22 (5.4.0 - 5.4.21)
Code Fix Example
Laravel API Security Remediation
<?php
// Vulnerable pattern (CVE-2017-9303)
$token = app('auth.password')->broker()->createToken($user);
$host = request()->getHost();
$resetUrl = 'https://' . $host . url('/password/reset', ['token' => $token, 'email' => urlencode($user->email)], true);
// Fixed pattern (do not trust request host; use configured app URL)
use Illuminate\\Support\\Facades\\URL;
URL::forceRootUrl(config('app.url'));
URL::forceScheme(parse_url(config('app.url'), PHP_URL_SCHEME));
$resetUrl = url('/password/reset', ['token' => $token, 'email' => $user->email], true);