MantisBT has a Content Security Policy bypass via attachments

Exploitation

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

CVSS 4.0

7.6 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-40597: 0.50% estimated exploitation activity in the next 30 days; percentile 42.75 (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.

Given any pre-existing XSS / HTML injection vulnerability, an attacker can bypass the Content Security Policy's script-src directive by uploading a crafted attachment to any issue that, when accessed via the filedownload.php link, will be downloaded with a valid JavaScript MIME type resulting in script execution. The uploaded payload must be sniffed as a valid JavaScript MIME type by PHP finfo (see filecreatefinfo() API function). Non-JavaScript MIME types will not get imported in a <script tag by the browser, due to response header X-Content-Type-Options being set to nosniff, which requires all imported JavaScript files to be a valid JavaScript MIME type. Impact Cross-site scripting Patches - 9e3bee2e7b909f4e3596985892b8bc8bee9e0bfe Workarounds None Credits Thanks to siunam (Tang Cheuk Hei) for discovering and responsibly reporting the issue.

Published by the source

11 May 2026, 19:34 UTC

Last modified by the source

8 Jun 2026, 23:20 UTC

Source last checked

26 Oct 2026, 14:48 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9c3j-xm6v-j7j3

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# Patch Next advisory brief: CVE-2026-40597

Advisory: MantisBT has a Content Security Policy bypass via attachments
IDs: CVE-2026-40597, GHSA-9c3j-xm6v-j7j3
Record: https://patchnext.com/advisories/cve-2026-40597 (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: High (CVSS 7.6)
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-9c3j-xm6v-j7j3 (GitHub-reviewed advisory GHSA-9c3j-xm6v-j7j3 lists affected ranges: Packagist mantisbt/mantisbt >=0 <=2.28.1)

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