Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
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 Network Sniffing (T1040); ranked at the 29th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SC-23 (Session Authenticity) and SC-8 (Transmission Confidentiality and Integrity) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
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.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-17455
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V10.4.16V10.5.1
Mitigating Controls (NIST 800-53 r5) AI
Session authenticity mechanisms directly stop replay of captured authentication traffic by enforcing freshness or cryptographic binding.
Transmission integrity (with anti-replay) stops captured messages from being accepted as valid later.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Protecting and verifying identity assertions prevents replay of captured authentication material.
Encryption and integrity protections for data-in-transit directly block capture-replay of credentials or tokens.
Network monitoring may detect anomalous replays after the fact but does not prevent the design flaw.
Strong authentication methods can reduce replay risk but do not inherently address captured messages.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Cryptographic protections (e.g., nonces, timestamps, message authentication codes) make captured authentication messages unusable for replay.
Secure authentication mechanisms directly prevent replay attacks by requiring fresh, non-replayable credentials or tokens.
Network security controls such as encryption and integrity protection reduce the feasibility of capturing and replaying authentication traffic.
Application security requirements can mandate replay-resistant authentication designs, but the control itself does not prescribe the technical measures.