CVE-2026-78587: Incorrect Authorization (CWE-863) in Fleet Server can lead to a denial of service of agent upload operations v

Routine

LOW 3.1UPGRADE

CVE-2026-78587 is a low-severity flaw (CVSS 3.1) affecting fleet server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	3.1 (Low)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.3% (top 78%)
CISA exploited list	No
Weakness	CWE-863
Published	2026-09-02
Last modified	2026-09-03

Publisher (CNA): Elastic · Vendor: elastic

Last updated 2026-09-03 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-02 15:17 UTCPublished CVE record published
2026-09-03 19:11 UTCUpdated Record last modified

elastic fleet server UPGRADE

Affected: >= 8.0.0 and < 8.19.16 · >= 9.0.0 and < 9.3.5 · >= 9.4.0 and < 9.4.2

Fixed in: 8.19.16, 9.3.5, 9.4.2

Safe to downgrade to: a release before 8.0.0

1. Check installed version

apt-cache policy fleet-server || rpm -q fleet-server || fleet-server --version

2. UPGRADE to 8.19.16 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade fleet-server

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade fleet-server

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 8.0.0 (Debian / Ubuntu)

apt-cache madison fleet-server sudo apt install fleet-server=<VERSION_BEFORE_8.0.0> sudo apt-mark hold fleet-server

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list fleet-server sudo dnf downgrade fleet-server-<VERSION_BEFORE_8.0.0> sudo dnf versionlock add fleet-server

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-78587?

fleet server: upgrade to 8.19.16, 9.3.5, 9.4.2. Exact commands for each OS are on this page.

Is CVE-2026-78587 being exploited?

CVE-2026-78587 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-78587 affect?

CVE-2026-78587 affects fleet server. Severity is low (CVSS 3.1). 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,

How urgent is CVE-2026-78587?

Priority 16/100. No elevated risk signals yet.

Related CVEs

CVE-2026-56150 MEDIUM 6.5 UPGRADE Allocation of Resources Without Limits or Throttling (CWE-770) in Fleet Server can lead to a denial of service
CVE-2026-72657 MEDIUM 6.5 UPGRADE Authorization Bypass Through User-Controlled Key (CWE-639) in Fleet Server can lead to information disclosure

References

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