CVE-2026-39960 MEDIUM

CVE-2026-39960: MantisBT is Vulnerable to Stored XSS through Custom Field Textarea Values

Vendor Mantisbt
Product mantisbt
Weakness CWE-79 · XSS
Published May 20, 2026
Last update May 21, 2026

CVSS base score

5.4/10
Attack vector Network
Attack complexity Low
Privileges required Low
User interaction Required
Confidentiality Low
Integrity Low

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

What the vulnerability does

01Description

Mantis Bug Tracker (MantisBT) is an open source issue tracker. Versions 2.28.1 and below contain flawed logic that causes improper escaping of a textarea custom field's contents in the Update Issue page, (bug_update_page.php) allowing an attacker to inject HTML and, if CSP settings permit, execute arbitrary JavaScript when the page is loaded. This facilitates session theft, leading to admin account takeover, full project data access. In order to exploit this issue, a textarea-type custom field must be configured for the project, the attack must be carried out by an authenticated user with bug report permission (low privilege). This can affect any user viewing the bug edit form, including administrators. The issue has been fixed in version 2.28.2. If users cannot immediately upgrade, they can work around the issue by using the default Content-Security Policy, which blocks script execution.

Key dates

02Disclosure timeline

May 20, 2026 CVE published
May 21, 2026 Record updated