What is CVE-2026-78587?

CVE-2026-78587 is a low-severity vulnerability in Elastic Fleet Server, classified under Incorrect Authorization. CVSS score: 3.1/10. Published 2026-09-02.

How severe is CVE-2026-78587?

Low severity. CVSS v3 base score is 3.1 out of 10.

Auth bypass in Elastic Fleet Server

CVE-2026-78587

Incorrect Authorization (CWE-863) in Fleet Server can lead to a denial of service of agent upload operations via Privilege Abuse (CAPEC-122). Fleet Server does not correctly verify session ownership during multi-part data upload operations, allowing any authenticated agent to interfere with the active upload sessions belonging to other enrolled agents.

Vulnerability class: Broken Access Control

Published 2026-09-02 · last modified 2026-09-03.

CVSS v3 metric

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

EPSS exploit prediction

EPSS: 0.003 (20.7th percentile), scored 2026-10-18.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 21st percentile — 20.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001

Affected products

Weakness classification (CWE)

CWE-863 — Incorrect Authorization

References

discuss.elastic.co/t/fleet-server-8-19-16-9-3-5-9-4-2-security-update-esa-2026-… (Vendor Advisory)

Frequently asked questions

What is CVE-2026-78587?: CVE-2026-78587 is a low-severity vulnerability in Elastic Fleet Server, classified under Incorrect Authorization. CVSS score: 3.1/10. Published 2026-09-02.
How severe is CVE-2026-78587?: Low severity. CVSS v3 base score is 3.1 out of 10.