In short
- CVE-2026-39960 is a MEDIUM (CVSS 5.4) vulnerability affecting mantisbt/mantisbt.
- Chance of exploitation in the next 30 days (EPSS): 0.23%, higher than 13.8% of all vulnerabilities.
- Fix: update to 2.28.2 or later.
Description
Improper escaping of a textarea custom field's contents in the Update Issue page (bug_update_page.php) allows an attacker to inject HTML and, if CSP settings permit, execute arbitrary JavaScript when the page is loaded.
Impact
Session theft leading to admin account takeover, full project data access.
- Precondition: A textarea-type custom field must be configured for the project
- Attacker: Authenticated user with bug report permission (low privilege)
- Victim: Any user viewing the bug edit form, including administrators
Patches
- 5fec0f448b7a7d7d539a6adb6dccceac4e4e4ab7
Workarounds
The default Content-Security Policy will block script execution.
References
Credits
Thanks to the following security researchers for independently discovering and responsibly reporting the issue, and providing a patch to fix it.
- Thanks to Nozomu Sasaki (Paul) (@morimori-dev)
- Tristan Madani (@TristanInSec) from Talence Security
NVD description
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.
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