---
id: CVE-2026-103415
title: >-
  When a TLS 1.3 client processes a HelloRetryRequest, it copies the server's
  cookie into its second ClientHello without checking that the cookie fits in
  the outgoing packet
summary: >-
  When a TLS 1.3 client processes a HelloRetryRequest, it copies the server's
  cookie into its second ClientHello without checking that the cookie fits in
  the outgoing packet. Both the length and the contents of that cookie come from
  the pe…
severity: critical
cvss: 9.3
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N'
cwe:
  - CWE-787
vendor: Eclipse Foundation
product: NetX Duo
affected:
  - netx_duo <= 6.5.1.202602
published: '2026-10-14'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T21:17:13.370'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-103415'
references:
  - url: >-
      https://github.com/eclipse-threadx/netxduo/security/advisories/GHSA-5pv3-rhf5-gwgq
    label: emo@eclipse.org
  - url: 'https://gitlab.eclipse.org/security/cve-assignment/-/work_items/357'
    label: emo@eclipse.org
tags:
  - nvd
  - cve.org
epss: 0.00284
epssPercentile: 0.21049
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-10-16T20:12:26.899295Z'
cvssSource: cna
ingestedAt: '2026-10-14T18:47:39.307Z'
---

## Overview

When a TLS 1.3 client processes a HelloRetryRequest, it copies the server's cookie into its second ClientHello without checking that the cookie fits in the outgoing packet. Both the length and the contents of that cookie come from the peer, and the write happens before certificate authentication completes, so a malicious or compromised server can overwrite memory past the caller supplied TLS packet buffer without presenting a certificate.



Only the client path is affected.

## Remediation

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