OpenVPN/openvpn

OpenVPN 2.7.4 Windows 11 fails TLS negotiation while 2.6.17 works

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#1,036 创建于 2026年5月18日

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描述

OpenVPN 2.7.4 on Windows 11 fails TLS negotiation with an existing legacy UDP setup that works correctly on:

  • Linux OpenVPN 2.6.14
  • Windows OpenVPN 2.6.17

Environment:

  • Windows 11 build 10.0.26200
  • OpenVPN 2.7.4
  • OpenSSL 3.6.2

Symptoms:

  • Client hangs at: TLS key negotiation failed to occur within 60 seconds
  • Server never logs: TLS: Initial packet from
  • tcpdump on intermediate pfSense shows repeated: UDP, length 14
  • No valid TLS handshake packets observed.

Same exact .ovpn config and certificates connect immediately with OpenVPN 2.6.17 on Windows and 2.6.14 on Linux.

Workaround: Downgrading Windows client from 2.7.4 to 2.6.17 resolves the issue instantly without configuration changes.

贡献者指南

技术栈
c
领域
security
议题类型
bug
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
4
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
3-5 days
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
fresh
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
C programmingTLS/SSL knowledgeOpenVPN architecture
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
35
研究方向
Start by comparing the git changelog between OpenVPN 2.6.17 and 2.7.4, focusing on commits related to TLS and Windows compatibility. Examine the TLS negotiation code in src/openvpn/ssl.c and ssl backend.c. Use tcpdump or Wireshark to capture the failing handshake and identify at which stage it stops. Check for any Windows specific changes in src/openvpn/win32.c and verify OpenSSL version upgrade impact.