mppx: Tempo has a session close voucher bypass vulnerability due to settled amount equality

Exploitation

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

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS

• CVE-2026-34209: 0.37% estimated exploitation activity in the next 30 days; percentile 31.27 (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.

Impact The tempo/session cooperative close handler validated the close voucher amount using < instead of <= against the on-chain settled amount. An attacker could submit a close voucher exactly equal to the settled amount, which would be accepted without committing any new funds, effectively closing or griefing the channel for free. Patches Fixed in 0.4.11. Workarounds There are no workarounds available for this vulnerability.

Published by the source

29 Mar 2026, 15:10 UTC

Last modified by the source

31 Mar 2026, 19:05 UTC

Source last checked

26 Oct 2026, 12:47 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-mv9j-8jvg-j8mr

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-mv9j-8jvg-j8mr

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# Patch Next advisory brief: CVE-2026-34209

Advisory: mppx: Tempo has a session close voucher bypass vulnerability due to settled amount equality
IDs: CVE-2026-34209, GHSA-mv9j-8jvg-j8mr
Record: https://patchnext.com/advisories/cve-2026-34209 (revision 2, source checked 26 Oct 2026, 12:47 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mppx 0.4.11. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm mppx: affected < 0.4.11; fixed in 0.4.11

## Suggested inspection (read-only)
- `npm ls mppx --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## 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 mppx.
- 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://osv.dev/vulnerability/GHSA-mv9j-8jvg-j8mr (OSV record GHSA-mv9j-8jvg-j8mr lists affected ranges: npm mppx >=0 <0.4.11 (fixed))
- Verified: https://github.com/advisories/GHSA-mv9j-8jvg-j8mr (GitHub-reviewed advisory GHSA-mv9j-8jvg-j8mr lists affected ranges: npm mppx >=0 <0.4.11)

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