Quick answers
- Is CVE-2026-78587 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-78587 being exploited in the wild.
- How severe is CVE-2026-78587?
- Low severity, with a CVSS score of 3.1, published 2 September 2026.
- Which products and versions are affected?
- Elastic Fleet Server 8.0.0 through 8.19.15, 9.0.0 through 9.3.4, 9.4.0 through 9.4.1.
- Is there a fix for CVE-2026-78587?
- A patch was published on 2026-09-02: Patched in Fleet Server 8.19.16, 9.3.5, and 9.4.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-78587 attacked?
- It is attacked over the network, in a hosted service.
- Am I affected by CVE-2026-78587?
- Check whether you run Elastic Fleet Server at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The vulnerability is an incorrect authorization flaw (CWE-863) in Fleet Server's multi-part data upload handling. The server fails to verify that an upload session belongs to the authenticated agent attempting to access it, allowing any enrolled agent to interfere with another agent's active upload sessions. The attack requires an attacker to be an authenticated agent with valid enrollment credentials but does not require administrator privileges. An attacker can disrupt agent uploads, preventing legitimate agents from submitting data. The issue is patched in Fleet Server versions 8.19.16, 9.3.5, and 9.4.2.
Affected products
- Elastic Fleet Server 8.0.0 through 8.19.15, 9.0.0 through 9.3.4, 9.4.0 through 9.4.1
Timeline
- 2026-09-02: disclosed
- 2026-09-02: patched: Patched in Fleet Server 8.19.16, 9.3.5, and 9.4.2