CVE-2025-27794

Flarum Vulnerable to Session Hijacking via Authoritative Subdomain Cookie Overwrite

Published Mar 12, 2025 CVSS 3.1 · 6.8 Medium EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
EUVD EUVD EUVD-2025-7808 Flarum Vulnerable to Session Hijacking via Authoritative Subdomain Cookie Overwrite
Github GHSA Github GHSA GHSA-hg9j-64wp-m9px Flarum Vulnerable to Session Hijacking via Authoritative Subdomain Cookie Overwrite
History
Type Values Removed Values Added
Metrics epss

{'score': 0.00067}

epss

{'score': 0.00083}

Type Values Removed Values Added
First Time appeared Flarum
Flarum flarum
CPEs cpe:2.3:a:flarum:flarum:*:*:*:*:*:*:*:*
Vendors & Products Flarum
Flarum flarum
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description 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.
Title Flarum Vulnerable to Session Hijacking via Authoritative Subdomain Cookie Overwrite
Weaknesses CWE-74
References
Metrics cvssV3_1

{'score': 6.8, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Mar 12, 2025, 3:29 PM
Reserved
Mar 6, 2025, 6:06 PM
Status
Analyzed
Published
Mar 12, 2025, 2:15 PM
Modified
Jun 17, 2026, 9:04 AM