Session voucher adding no new funds is accepted without a charge in mpp, serving paid resources for free (CVE-2026-89420) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-89420

Session voucher adding no new funds is accepted without a charge in mpp, serving paid resources for free

Answer in brief

CVE-2026-89420 records a Unknown severity vulnerability in Session voucher adding no new funds is accepted without a charge in mpp, serving paid resources for free. The current sources do not mark it as known exploited. The current feed maps ZenHive/mpp (generic), ZenHive/mpp (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 22, 2026Updated Sep 22, 2026Source checked Sep 22, 2026First seen by HOL Sep 22, 2026Material review Sep 22, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps ZenHive/mpp (generic), ZenHive/mpp (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
ZenHive/mppgeneric	>=0.14.0 <0.16.2	0.16.2
ZenHive/mppgeneric	>=82df569c898be1137189e3648e1edb4af6363651 <7270edc1dcfb58250cc5ee812876609206564165	7270edc1dcfb58250cc5ee812876609206564165

Recommended response

Check inventory. Check lockfiles and deployed manifests for ZenHive/mpp, ZenHive/mpp.
Review the reported fix. Update ZenHive/mpp to 0.16.2; ZenHive/mpp to 7270edc1dcfb58250cc5ee812876609206564165 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 22, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.