CVE-2025-27794

CVE-2025-27794 · Flarum Vulnerable to Session Hijacking via Authoritative Subdomain Cookie Overwrite

This page contains facts from public vulnerability sources. Check the original advisory before updating.

Flarum is open-source forum software. A session hijacking vulnerability exists in versions prior to 1.8.10 when an attacker-controlled authoritative subdomain under a parent domain (e.g., `subdomain.host.com`) sets cookies scoped to the parent domain (`.host.com`). This allows session token replacement for applications hosted on sibling subdomains (e.g., `community.host.com`) if session tokens aren't rotated post-authentication. Key Constraints are that the attacker must control any subdomain under the parent domain (e.g., `evil.host.com` or `x.y.host.com`), and the parent domain must not be on the Public Suffix List. Due to non-existent session token rotation after authenticating we can theoretically reproduce the vulnerability by using browser dev tools, but due to the browser's security measures this does not seem to be exploitable as described. Version 1.8.10 contains a patch for the issue.

CVSS 6.8 · Medium · EPSS 0.5% · Fix available

Published

2025-03-12T14:00:21.862Z

Updated

2025-03-12T15:29:21.831Z

Stack: php

Check your server →