CVE-2026-39960
MantisBT is Vulnerable to Stored XSS in Custom Field Textarea Values
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 - https://mantisbt.org/bugs/view.php?id=37003 - This is related to [CVE-2024-34081](https://github.com/advisories/GHSA-wgx7-jp56-65mq). ### 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
How to fix CVE-2026-39960
To remediate CVE-2026-39960, upgrade the affected package to a fixed version below.
- —upgrade to 2.28.2 or later
Is CVE-2026-39960 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- from 0, < 2.28.2
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM5.4 | CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N |