ZenHive mpp up to 0.16.1 Accept Voucher actions.ex MPP.Session.Actions.accept_voucher authentication replay

Summaryinfo

A vulnerability classified as critical has been found in ZenHive mpp up to 0.16.1. Affected is the function MPP.Session.Actions.accept_voucher of the file lib/mpp/session/actions.ex of the component Accept Voucher. The manipulation leads to authentication replay. This vulnerability is uniquely identified as CVE-2026-89420. The attack is possible to be carried out remotely. No exploit exists. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in ZenHive mpp up to 0.16.1 and classified as critical. This issue affects the function MPP.Session.Actions.accept_voucher of the file lib/mpp/session/actions.ex of the component Accept Voucher. The manipulation with an unknown input leads to a authentication replay vulnerability. Using CWE to declare the problem leads to CWE-294. 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). Impacted is confidentiality, integrity, and availability. The summary by CVE is:

Improper Validation of Specified Quantity in Input in ZenHive mpp allows a client holding an open payment channel to obtain paid resources without being charged. MPP.Session.Actions.accept_voucher/3 in lib/mpp/session/actions.ex treats a voucher whose cumulativeAmount equals the channel's already-accepted cumulative amount as an idempotent success, returning the channel unchanged without calling maybe_spend/2. The credential verifies, the protected resource is served, and spent and units stay where they were. Because the server issues a fresh challenge per request and the credential replay store keys on challenge id and payload, the same signed voucher can be re-presented under every new challenge, so one paid voucher yields an unbounded number of paid units. The path is reachable from any method built on MPP.Session.Method through the Plug, MCP, JSON-RPC and WebSocket transports. This issue affects mpp: from 0.14.0 before 0.16.2.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-89420 since 09/11/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1040 according to MITRE ATT&CK.

Upgrading to version 0.16.2 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-84360). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Vendor

• ZenHive

Name

• mpp

Version

• 0.16.0
• 0.16.1

Website

• Product: https://github.com/ZenHive/mpp/

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Be aware that VulDB is the high quality source for vulnerability data.

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