# Fleet Server 8.19.16, 9.3.5, 9.4.2 Security Update (ESA-2026-164) **URL:** \ **Category:** Security Announcements\ **Created:** [September 1, 2026, 10:36pm UTC](https://discuss.elastic.co/t/fleet-server-8-19-16-9-3-5-9-4-2-security-update-esa-2026-164/390117 "2026-09-01T22:36:19Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![Bryan\_Garcia](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/bryan_garcia/32/148179_2.png) [@Bryan\_Garcia](https://discuss.elastic.co/u/Bryan_Garcia)\ **Post date:** [September 1, 2026, 10:36pm UTC](https://discuss.elastic.co/t/fleet-server-8-19-16-9-3-5-9-4-2-security-update-esa-2026-164/390117/1 "2026-09-01T22:36:19Z")
**Incorrect Authorization in Fleet Server Leading to Denial of Service of Agent Upload Operations** 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. **Affected Versions:** - 8.x: All versions from 8.0.0 up to and including 8.19.15 - 9.x: - All versions from 9.0.0 up to and including 9.3.4 - All versions from 9.4.0 up to and including 9.4.1 **Affected Configurations:** All configurations are affected. **Solutions and Mitigations:** The issue is resolved in Fleet Server versions 8.19.16, 9.3.5, and 9.4.2. **For Users that Cannot Upgrade:** There are no workarounds for this vulnerability. **Indicators of Compromise (IOC)** No specific indicators of compromise have been identified for this vulnerability. **Severity:** CVSSv3.1: Low ( 3.1 ) - CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L **CVE ID:** CVE-2026-78587 **Problem Type:** CWE-863 - Incorrect Authorization **Impact:** CAPEC-122 - Privilege Abuse