What is CVE-2026-18420?

CVE-2026-18420 is a high-severity vulnerability in AWS Amazon Opensearch Service, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 8.8/10. Published 2026-08-20.

How severe is CVE-2026-18420?

High severity. CVSS v3 base score is 8.8 out of 10.

Prototype Pollution in AWS Amazon Opensearch Service

CVE-2026-18420

Improper input validation in the Time Series Visual Builder (TSVB) plugin in OpenSearch Dashboards allows an authenticated remote user to execute arbitrary code on the server via a crafted JSON payload to the metrics visualization API endpoint. This issue is a form of prototype pollution that enables remote code execution. To remediate this issue, users should upgrade to OpenSearch Dashboards 3.8 or later.

Vulnerability class: Prototype Pollution

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

Affected products

Weakness classification (CWE)

CWE-1321 — Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution)

References

ff89ba41-3aa1-4d27-914a-91399e9639e5 (patch)
ff89ba41-3aa1-4d27-914a-91399e9639e5 (third-party-advisory)
ff89ba41-3aa1-4d27-914a-91399e9639e5 (vendor-advisory)

Frequently asked questions

What is CVE-2026-18420?: CVE-2026-18420 is a high-severity vulnerability in AWS Amazon Opensearch Service, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 8.8/10. Published 2026-08-20.
How severe is CVE-2026-18420?: High severity. CVSS v3 base score is 8.8 out of 10.