CVE-2025-1220: Hostname Validation in PHP 8.1-8.4

The core of the vulnerability lies in the lack of null character validation within the hostname parameter of functions like fsockopen(). When a malicious hostname containing null characters is supplied, parse_url() may interpret it differently than intended. This can lead to bypasses of access control mechanisms that rely on the hostname for validation. An attacker could craft a malicious hostname to manipulate the URL parsing process, potentially gaining unauthorized access to resources or executing unintended code. While the CVSS score is LOW, the potential for bypasses in custom applications warrants careful attention and remediation.

1. Reserved2025-02-11
2. Published2025-07-13
3. Modified2025-11-04
4. EPSS updated2026-04-02

The primary mitigation for CVE-2025-1220 is to upgrade to a patched version of PHP. Specifically, upgrade to PHP 8.4.10 or later. If upgrading is not immediately feasible, consider implementing stricter input validation within your application code to sanitize hostnames before passing them to functions like fsockopen() and parseurl(). This should include explicit checks for null characters and other potentially malicious characters. Web Application Firewalls (WAFs) configured to inspect and filter HTTP headers could also provide a layer of defense, but should not be relied upon as the sole mitigation. After upgrading, confirm the fix by attempting to use a crafted hostname containing null characters with fsockopen() and verifying that parseurl() behaves as expected.