#VU126534 Session Fixation in Flarum - CVE-2025-27794
Published: March 12, 2025 / Updated: April 20, 2026
Vulnerability identifier: #VU126534
Vulnerability risk: Medium
CVSSv4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2025-27794
CWE-ID: CWE-384
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerable software:
Flarum
Flarum
Software vendor:
Flarum
Flarum
Description
The vulnerability allows a remote attacker to hijack a user's session.
The vulnerability exists due to improper session management in session token handling when an attacker-controlled authoritative subdomain sets cookies scoped to the parent domain. A remote attacker can set a crafted cookie containing the attacker's session token to hijack a user's session.
User interaction is required, and exploitation is possible only when the parent domain is not on the Public Suffix List and the attacker controls a direct child subdomain.
Remediation
Install security update from vendor's website.