Zephyr Project warns of a critical vulnerability

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[TLP:CLEAR] Zephyr Project warns of a critical vulnerability

Zephyr Project warns of a critical vulnerability in the Zephyr operating system [1], specifically in the HTTP server path for upgrading to WebSocket. At the time of the announcement, the vendor does not list a released fixed version; however, source code fixes are available in the main branch [2] and in a backport for v4.3 [3].

Zephyr RTOS - out-of-bounds read/write, DoS, RCE (CVE-2026-5067)

CVSS 9.8 (Critical)

An unauthenticated remote attacker can trigger out-of-bounds reads and writes of stack memory, perform a DoS attack and potentially execute arbitrary code due to improper handling of the Sec-WebSocket-Key header [1].

The vulnerability is present in product:

Zephyr; >= 3.7.0, <= 4.3.0

CVSS: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

More information:

CVE-2026-5067 at cve.org, NVD
CWE-170: Improper Null Termination at cwe.mitre.org
CWE-787: Out-of-bounds Write at cwe.mitre.org

The vulnerability was publicly disclosed 9. 6. 2026.

Links

By CESNET, z.s.p.o. Michaela Jarošová on 9. 6. 2026.

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[TLP:CLEAR] Zephyr Project warns of a critical vulnerability

Zephyr RTOS - out-of-bounds read/write, DoS, RCE (CVE-2026-5067)

CVSS 9.8 (Critical)

Links