CVE-2026-89420

See a problem?
Please try reporting it to the source first.
Source
https://cve.org/CVERecord?id=CVE-2026-89420
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89420.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-89420
Aliases
Published
2026-09-22T11:16:29Z
Modified
2026-09-24T03:46:58Z
Severity
  • 7.1 (High) CVSS_V4 - 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 CVSS Calculator
Summary
Session voucher adding no new funds is accepted without a charge in mpp, serving paid resources for free
Details

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.

Database specific 
{
    "cna_assigner":  "EEF",
    "cwe_ids":  [
        "CWE-1284"
    ],
    "osv_generated_from":  "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89420.json",
    "unresolved_ranges":  [
        {
            "extracted_events":  [
                {
                    "introduced":  "82df569c898be1137189e3648e1edb4af6363651"
                },
                {
                    "fixed":  "7270edc1dcfb58250cc5ee812876609206564165"
                }
            ],
            "source":  "AFFECTED_FIELD"
        }
    ]
}
References

Affected packages

Git / github.com/zenhive/mpp

Affected ranges

Type
GIT
Repo
https://github.com/zenhive/mpp
Events
Introduced
ad394b7df40e014eefb9f2f5ca2127326a005c3f
Fixed
3b7e43abf60fa30c40985e4043965ec67791b4dc
Fixed
7270edc1dcfb58250cc5ee812876609206564165
Fixed
82df569c898be1137189e3648e1edb4af6363651
Database specific
Show details 
{
    "extracted_events":  [
        {
            "introduced":  "0.14.0"
        },
        {
            "fixed":  "0.16.2"
        }
    ],
    "source":  [
        "DESCRIPTION",
        "REFERENCES"
    ]
}

Affected versions

v0.*
v0.14.0
v0.15.0
v0.16.0
v0.16.1

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89420.json"