CVE-2026-39960

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.

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.

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

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

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-39960 has a CVSS score of 5.4 (Medium). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.28.2); upgrading removes the vulnerable code path.

Kodem intelligence

• 5fec0f448b7a7d7d539a6adb6dccceac4e4e4ab7

1. What is CVE-2026-39960? CVE-2026-39960 is a medium-severity cross-site scripting (XSS) vulnerability in mantisbt/mantisbt (composer), affecting versions <= 2.28.1. It is fixed in 2.28.2. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-39960? CVE-2026-39960 has a CVSS score of 5.4 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of mantisbt/mantisbt are affected by CVE-2026-39960? mantisbt/mantisbt (composer) versions <= 2.28.1 is affected.
4. Is there a fix for CVE-2026-39960? Yes. CVE-2026-39960 is fixed in 2.28.2. Upgrade to this version or later.
5. Is CVE-2026-39960 exploitable, and should I be worried? Whether CVE-2026-39960 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-39960 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-39960? Upgrade mantisbt/mantisbt to 2.28.2 or later.