CVE-2026-89420
Session voucher adding no new funds is accepted without a charge in mpp, serving paid resources for free
- State
- Published
- Severity
- 7.1 High
- Published
- Sep 22, 2026
- Updated
- Sep 22, 2026
- Reserved
- Sep 11, 2026
Description
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 7.1 High | CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N | EEF |
Weaknesses
- CWE-1284 Improper Validation of Specified Quantity in Input
Affected Products
| Product | Versions |
|---|---|
mppZenHive |
|
mppZenHive |
|
References
- GitHub Advisoryrelatedvendor-advisory
- EEF CNA record for CVE-2026-89420related
- OSV record EEF-CVE-2026-89420related
- Introducing commit 82df569 in ZenHive/mpprelated
- Fix commit 7270edc in ZenHive/mpppatch
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