---
id: CVE-2026-1677
title: >-
  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
summary: >-
  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_mi…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N'
cwe:
  - CWE-757
vendor: zephyrproject
product: zephyr
affected:
  - zephyr <= 4.3.0
published: '2026-05-11'
updated: '2026-07-08'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-1677'
references:
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-23r2-m5wx-4rvq
    label: vulnerabilities@zephyrproject.org
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-23r2-m5wx-4rvq
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.00243
epssPercentile: 0.15841
ingestedAt: '2026-07-08T13:51:10.740Z'
---

## Overview

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

- `zephyr <= 4.3.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.