Low severity · published Sep 2, 2026
CVE-2026-78587
Incorrect Authorization in Fleet Server Leading to Denial of Service of Agent Upload Operations
3.1
CVSS
0.3%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
Attack vector
Network
Complexity
High
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
None
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 22% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FS
Fleet Server · Elastic
8.0.0 through 8.19.15; 9.0.0 through 9.3.4; 9.4.0 through 9.4.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-78587
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-78587
Vendor Advisory
https://discuss.elastic.co/t/fleet-server-8-19-16-9-3-5-9-4-2-security-update-esa-2026-164/390117
More from Fleet Server
9.1
CVE-2026-72676
Improper Control of Generation of Code in Fleet Server Leading to Code Injection
8.1
CVE-2023-46667
An issue was discovered in Fleet Server >= v8.10.0 and < v8.10.3 where Agent enrolment tokens are being inserted into the Fleet Server’s log file in plain text
7.5
CVE-2026-56150
Allocation of Resources Without Limits or Throttling in Fleet Server Leading to Denial of Service
6.5
CVE-2026-72657
Authorization Bypass Through User-Controlled Key in Fleet Server Leading to Information Disclosure