CVE-2026-39960 MantisBT is Vulnerable to Stored XSS through Custom Field Textarea Values
Authenticated attackers can inject malicious scripts via custom field textareas, potentially stealing sessions and gaining admin access in MantisBT.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-39960?
CVE-2026-39960 is a medium-severity cross-site scripting vulnerability in mantisbt, published on 20 May 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-79
Which versions are affected by CVE-2026-39960?
2 open source packages ship an affected version, including mantisbt/mantisbt.
| Package | Affected | Fixed in |
|---|---|---|
mantisbt/mantisbt Packagist | All versions | 2.28.2 |
mantisbt/mantisbt Packagist | All versions | 2.28.2 |
How do I fix CVE-2026-39960?
Upgrade mantisbt/mantisbt to 2.28.2 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-39960 being exploited?
There is no known exploitation of CVE-2026-39960 in the wild and no public exploit code.
Sources
Also known as GHSA-qj6w-v29q-4rgx.