mpp: Authentication Bypass by Capture-replay
CVE-2026-67581 is a high-severity authentication bypass by capture-replay vulnerability in mpp from ZenHive, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 0.6.3, ecc038088b1cda09ad8a84acc6cc112addb4a68f as the first without the flaw, so updating mpp to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.6% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update mpp to 0.6.3 or ecc038088b1cda09ad8a84acc6cc112addb4a68f, whichever matches your release line, or a later version.
- Update Machine Payments Protocol to 0.6.4 or a later version.
- Read the advisory on github.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| ZenHive | mpp | 0.3.0 up to, but not including, 0.6.3; 65b9e425ce27631c786a5b380b5e4c5ae607ec6d up to, but not including, ecc038088b1cda09ad8a84acc6cc112addb4a68f | 0.6.3, ecc038088b1cda09ad8a84acc6cc112addb4a68f |
| Zenhive | Machine Payments Protocol | 0.3.0 up to, but not including, 0.6.4 | 0.6.4 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.7 | High | CNA |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
Authentication Bypass by Capture-replay in ZenHive mpp allows an unauthenticated remote client to obtain paid resources by resubmitting one settled on-chain transfer. MPP.Methods.EVM.verify/2 accepts a transaction-hash credential and matches a transfer purely on token, to and amount (ERC-20) or to and value (native). It binds the proof neither to the challenge being verified nor to any record of prior use, and the generic MPP.Plug dedup store keys on challenge.id, which is regenerated for every 402 response. On a static-price route, a single historical transfer matching the charge therefore satisfies an unbounded number of later charges, including transfers an attacker can read off a public block explorer. This issue affects mpp: from 0.3.0 before 0.6.3.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Authentication Bypass by Capture-replay
A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes).
How developers prevent this class of flaw
- Utilize some sequence or time stamping functionality along with a checksum which takes this into account in order to ensure that messages can be parsed only once.
- Since any attacker who can listen to traffic can see sequence numbers, it is necessary to sign messages with some kind of cryptography to ensure that sequence numbers are not simply doctored along with content.
More Authentication Bypass by Capture-replay vulnerabilities (CWE-294)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Third-party and government advisories
- cna.erlef.org/cves/CVE-2026-67581.htmlThird Party Advisory
- osv.dev/vulnerability/EEF-CVE-2026-67581Third Party Advisory
Other vulnerabilities in mpp
- 7.1 High severity
- 8.2 High severity
- 8.3 High severity
- 8.3 High severity
- 8.2 High severity
- 7.5 High severity
Recent Authentication Bypass by Capture-replay vulnerabilities
- 7.4 High severity
- 7.7 High severity
- 8.1 High severity
- 8.1 High severity
- 8.8 High severity
- 9.8 Critical severity
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