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High, CVSS 7.2

MantisBT is Vulnerable to XSS leading to account takeover via updating a user's font family preference

CVE-2026-40596GHSA-j3v9-553h-x28j

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (mantisbt/mantisbt 2.28.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
7.2 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:H/VI:L/VA:L/SC:H/SI:H/SA:L · score source
EPSS
  • CVE-2026-40596: 0.42% estimated exploitation activity in the next 30 days; percentile 36.74 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Any authenticated user can inject arbitrary HTML via updating their account's font family. Impact Cross-site scripting. The injected payload will be reflected in every MantisBT page. Leveraging another vulnerability (CSP bypass, see GHSA-9c3j-xm6v-j7j3), the attacker could achieve account takeover. Patches - 9e8409cdd979eba86ef532756fc47c1d8112d22d Workarounds None Credits Thanks to siunam (Tang Cheuk Hei) for discovering and responsibly reporting the issue.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-j3v9-553h-x28j

Agent brief

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# Patch Next advisory brief: CVE-2026-40596

Advisory: MantisBT is Vulnerable to XSS leading to account takeover via updating a user's font family preference
IDs: CVE-2026-40596, GHSA-j3v9-553h-x28j
Record: https://patchnext.com/advisories/cve-2026-40596 (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 7.2)
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 >= 2.11.0, <= 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-j3v9-553h-x28j (GitHub-reviewed advisory GHSA-j3v9-553h-x28j lists affected ranges: Packagist mantisbt/mantisbt >=2.11.0 <=2.28.1)

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