CVE-2026-34209: mppx: Tempo has a session close voucher bypass vulnerability due to settled amount equality

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-31 · updated 2026-07-24
Weakness: CWE-294

Description

mppx is a TypeScript interface for machine payments protocol. Prior to version 0.4.11, 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. This issue has been patched in version 0.4.11.

Affected products

wevm mppx: before 0.4.11 — fixed in 0.4.11

How to fix

Upgrade to a fixed version: wevm mppx 0.4.11. Check the vendor advisory for mitigations.

References

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