---
id: CVE-2026-8718
title: >-
  Out-of-bounds write in DTLS peer Connection ID getsockopt
  (`TLS_DTLS_PEER_CID_VALUE`) in Zephyr net sockets/TLS
summary: >-
  tls_opt_dtls_peer_connection_id_value_get() in
  subsys/net/lib/sockets/sockets_tls.c, which handles getsockopt(SOL_TLS,
  TLS_DTLS_PEER_CID_VALUE), passed the caller-supplied optval directly to
  mbedtls_ssl_get_peer_cid() without verifying t…
severity: high
cvss: 8.4
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-787
vendor: zephyrproject
product: zephyr
affected:
  - zephyr >= 3.5.0 < 4.3.2
  - zephyr >= 4.4.0 < 4.4.1
ssvc:
  exploitation: poc
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-08-12T18:49:17.354008Z'
exploitAvailable: true
published: '2026-08-10'
updated: '2026-11-04'
sourceUpdated: '2026-11-04T04:59:18.089Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-8718'
references:
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/commit/aa317825a55a401315e8e17f620c70c02e8f176d
    label: Fix commit
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-p3r6-mx6c-33gq
    label: GHSA-p3r6-mx6c-33gq
tags:
  - cve.org
  - exploit-available
epss: 0.00171
epssPercentile: 0.06491
ingestedAt: '2026-11-05T20:33:06.699Z'
---

## Overview

tls_opt_dtls_peer_connection_id_value_get() in subsys/net/lib/sockets/sockets_tls.c, which handles getsockopt(SOL_TLS, TLS_DTLS_PEER_CID_VALUE), passed the caller-supplied optval directly to mbedtls_ssl_get_peer_cid() without verifying the buffer was at least MBEDTLS_SSL_CID_OUT_LEN_MAX (default 32) bytes. mbedtls_ssl_get_peer_cid() copies the peer-negotiated DTLS Connection ID (length 1..MBEDTLS_SSL_CID_OUT_LEN_MAX) into that buffer without a destination-size parameter, so a caller-supplied optlen smaller than the CID causes a write of up to 31 bytes past the buffer end.

In CONFIG_USERSPACE builds the getsockopt syscall verifier (z_vrfy_zsock_getsockopt) bounce-buffers the user's optval into a kernel allocation of exactly optlen bytes (k_usermode_alloc_from_copy -> z_thread_malloc), so an unprivileged user thread that passes a small optlen on a connected DTLS socket with Connection ID enabled induces a kernel-heap buffer overflow, with the overflowing content being the remote peer's CID.

The defect requires CONFIG_MBEDTLS_SSL_DTLS_CONNECTION_ID, an established DTLS session with a negotiated peer CID, and (for the kernel-crossing case) CONFIG_USERSPACE. Introduced when the TLS_DTLS_CID option was added (v3.5.0).

The fix rejects callers whose optlen is below MBEDTLS_SSL_CID_OUT_LEN_MAX with -EINVAL.

## Affected

- `zephyr >= 3.5.0 < 4.3.2`
- `zephyr >= 4.4.0 < 4.4.1`

## Remediation

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