CVE-2026-1677 zephyrproject-rtos CVE debrief

Who should care

Organizations using Zephyr for TLS 1.3 connections should be aware of this vulnerability. Specifically, those who have enabled both TLS 1.2 and TLS 1.3 in their Kconfig settings and rely on `IPPROTO_TLS_1_3` for secure connections may be affected.

Technical summary

The vulnerability arises from the lack of propagation of socket-level protocol selection to mbedTLS. When creating a socket with `IPPROTO_TLS_1_3`, the ClientHello message advertises both TLS 1.2 and TLS 1.3. If the peer supports both versions, it may establish a TLS 1.2 connection, bypassing the intended security of TLS 1.3. This can lead to exposure to TLS 1.2-specific vulnerabilities. A workaround is available using the `TLS_CIPHERSUITE_LIST` socket option to restrict cipher suites to TLS 1.3-only.

Defensive priority

Medium priority should be given to addressing this vulnerability, especially for applications relying on TLS 1.3 for security.

Recommended defensive actions

• Review and update Kconfig settings to ensure proper TLS version enforcement.
• Implement the workaround using `TLS_CIPHERSUITE_LIST` socket option to restrict to TLS 1.3 cipher suites.
• Monitor for and apply patches or updates from Zephyr as they become available.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.

Evidence notes

The CVE record and NVD details provide information on the vulnerability. The vendor advisory on GitHub offers additional context and mitigation strategies. Evidence is limited to public sources and may not cover all affected systems or specific configurations. Defenders should verify system configurations, review Kconfig settings, and assess exposure based on TLS version usage.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.