CVE-2026-5067: Zephyrproject Zephyr

Critical severity, CVSS 9.8. EPSS: 0.9% chance of exploitation in the next 30 days.

A remote, unauthenticated attacker can trigger memory corruption in Zephyr's HTTP server WebSocket upgrade path by sending a crafted Sec-WebSocket-Key header. The HTTP/1 header parser copies the header into a fixed-size buffer using a bounded copy that does not guarantee NUL termination when the input length reaches the buffer size. During upgrade handling the buffer is copied to a local stack buffer and passed to strlen(); if no NUL exists in-bounds, strlen() reads beyond the stack buffer and subsequent concatenation with the WebSocket magic string can write out of bounds. This leads to out-of-bounds read and write on stack memory, resulting in crash (denial of service) and potentially code execution. The path is reachable when CONFIG_HTTP_SERVER_WEBSOCKET is enabled.

Affected products

• Zephyrproject Zephyr: from 3.7.0, up to and including 4.3.0

Published 2026-06-09. Last modified 2026-07-23.