# CVE-2026-1677: net: TLS 1.2 connections allowed on TLS 1.3 sockets


- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 11 May 2026
- **Updated:** 15 Oct 2026
- **Also known as:** GHSA-23r2-m5wx-4rvq

## What is CVE-2026-1677?

CVE-2026-1677 is a medium-severity vulnerability in Zephyrproject Zephyr, published on 11 May 2026. 

### 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.

Weakness: CWE-757 (Selection of Less-Secure Algorithm During Negotiation)

## Which versions are affected by CVE-2026-1677?

It affects 1 product.


Products: Zephyrproject Zephyr.

## How do I fix CVE-2026-1677?

No fix has been published for CVE-2026-1677 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-1677 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-1677 exists.

## Other vulnerabilities in Zephyrproject Zephyr

- [CVE-2026-5067](https://insights.sbomify.com/CVE-2026-5067/): Out-of-bounds read/write in HTTP WebSocket upgrade via non-null-terminated Sec-WebSocket-Key (critical 9.8)
- [CVE-2022-3806](https://insights.sbomify.com/CVE-2022-3806/): Bluetooth HCI Error Handling Double Free (critical 9.8)
- [CVE-2017-14199](https://insights.sbomify.com/CVE-2017-14199/): Memory corruption in getaddrinfo (critical 9.8)
- [CVE-2018-1000800](https://insights.sbomify.com/CVE-2018-1000800/): Null dereference in n/a (critical 9.8)
- [CVE-2021-3329](https://insights.sbomify.com/CVE-2021-3329/): DOS: Incorrect handling of the initial HCI ACL_MTU handshake packet leads to crash of bluetooth host layer (critical 9.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-1677 and fix it if it is affected.

What it is: CVE-2026-1677 is a medium-severity vulnerability in Zephyrproject Zephyr, published on 11 May 2026. 
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-1677 exists.

Affected product: Zephyrproject Zephyr. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-1677/ (Markdown: https://insights.sbomify.com/CVE-2026-1677/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-1677
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-1677
- OSV: https://osv.dev/vulnerability/CVE-2026-1677

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-1677/
Summaries are generated and may contain mistakes; the official description above is the record.