CVE-2026-34209

High

Published: 31 March 2026

Published

31 March 2026

Modified

03 April 2026

KEV Added

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Patch

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

EPSS Score 0.0001 2.1th percentile

Risk Priority 15 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-34209 is a high-severity Authentication Bypass by Capture-replay (CWE-294) vulnerability in Wevm Mppx. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 2.1th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Application or System Exploitation (T1499.004). What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Requires timely identification, testing, and implementation of fixes for the specific logic flaw in close voucher validation, as patched in mppx 0.4.11.

SI-10 Information Input Validation good match

prevent

Enforces rigorous information input validation mechanisms to correctly compare close voucher amounts using <= against on-chain settled amounts, preventing invalid acceptance.

RA-5 Vulnerability Monitoring and Scanning partial match

detect

Provides vulnerability scanning to identify the presence of CVE-2026-34209 in mppx dependencies, enabling proactive remediation.

MITRE ATT&CK Enterprise TechniquesAI

T1499.004 Application or System Exploitation Impact

Adversaries may exploit software vulnerabilities that can cause an application or system to crash and deny availability to users.

attack.mitre.org →

Why these techniques?

The logic flaw enables remote unauthenticated exploitation of the payment channel close handler to disrupt cooperative close and deny service to participants via application exploitation.

Confidence: MEDIUM · MITRE ATT&CK Enterprise v18.1

NVD 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.

Deeper analysisAI

CVE-2026-34209 affects mppx, a TypeScript interface for the machine payments protocol, in versions prior to 0.4.11. The vulnerability resides in the tempo/session cooperative close handler, which incorrectly validated the close voucher amount using a strict less-than operator ("<") instead of less-than-or-equal-to ("<=") when comparing it against the on-chain settled amount. This logic flaw, classified under CWE-294 (Unevaluated Code), carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N), indicating high integrity impact with no confidentiality or availability effects.

Any unauthenticated attacker with network access can exploit this vulnerability by submitting a close voucher with an amount exactly equal to the on-chain settled amount. The invalid comparison allows the voucher to be accepted without requiring the attacker to commit any additional funds, enabling them to unilaterally close the payment channel or grief it for free, disrupting the cooperative close process and potentially denying service to legitimate participants.

The issue has been addressed in mppx version 0.4.11, where the validation logic was corrected to use "<=" as detailed in the patching commit at https://github.com/wevm/mppx/commit/94088246ee18f21b5d6be40d9e7a464f5a280bfb. Security practitioners should upgrade to this version or later, with further details available in the release notes at https://github.com/wevm/mppx/releases/tag/mppx@0.4.11 and the GitHub security advisory at https://github.com/wevm/mppx/security/advisories/GHSA-mv9j-8jvg-j8mr.