Vulnerability · Published May 11, 2026 · Assigned by zephyr
CVE-2026-1677net: TLS 1.2 connections allowed on TLS 1.3 sockets
Medium 5.3
In plain English
A medium-severity security flaw in Zephyr from zephyrproject-rtos. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 16% of all known vulnerabilities).
Official description
Zephyr sockets created with `IPPROTO_TLS_1_3` can still negotiate a TLS 1.2 connection when both TLS versions are enabled in Kconfig, because the socket-level protocol selection is not propagated to mbedTLS (e.g. via `mbedtls_ssl_conf_min_tls_version`). The ClientHello advertises both versions and the peer can establish TLS 1.2, so applications that assumed `IPPROTO_TLS_1_3` enforces TLS 1.3 may silently use TLS 1.2 and remain exposed to TLS 1.2-specific weaknesses. As a workaround, the `TLS_CIPHERSUITE_LIST` socket option can be restricted to TLS 1.3-only cipher suites.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| zephyrproject-rtos | Zephyr | * – before 4.4.0 |
Weakness: CWE-757 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N