MantisBT is Vulnerable to Stored XSS in Custom Field Textarea Values

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-39960: 0.23% estimated exploitation activity in the next 30 days; percentile 13.87 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Improper escaping of a textarea custom field's contents in the Update Issue page (bugupdatepage.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. 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…

Published by the source

11 May 2026, 19:34 UTC

Last modified by the source

8 Jun 2026, 20:14 UTC

Source last checked

26 Oct 2026, 14:48 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-qj6w-v29q-4rgx

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# Patch Next advisory brief: CVE-2026-39960

Advisory: MantisBT is Vulnerable to Stored XSS in Custom Field Textarea Values
IDs: CVE-2026-39960, GHSA-qj6w-v29q-4rgx
Record: https://patchnext.com/advisories/cve-2026-39960 (revision 1, source checked 26 Oct 2026, 14:48 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mantisbt/mantisbt 2.28.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist mantisbt/mantisbt: affected <= 2.28.1; fixed in 2.28.2

## Suggested inspection (read-only)
- Packagist mantisbt/mantisbt: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on mantisbt/mantisbt.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-qj6w-v29q-4rgx (GitHub-reviewed advisory GHSA-qj6w-v29q-4rgx lists affected ranges: Packagist mantisbt/mantisbt >=0 <=2.28.1)

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