Breaking VLESS changes with one of latest PRs

[kastov]

VLESS connections using xtls-rprx-vision flow fail when using the latest Xray Core version with Mihomo clients running core version below v1.9.12. Connections result in "ERR_EMPTY_RESPONSE" or "ERR_CONNECTION_CLOSED" errors.

Cause

I debugged a few commits after v25.8.31 and found problem PR.

Issue introduced in PR: #5076, to be precise: 4064f8d

Steps to reproduce

1. Install latest Xray Core
2. Install Clash Verge (Mihomo v1.9.2) or any Mihomo client with core version < v1.9.12
3. Configure Xray with:
   • Protocol: VLESS+TLS or VLESS+REALITY
   • Flow: xtls-rprx-vision
4. Attempt to access websites such as:
   • https://code.visualstudio.com
   • https://productionresultssa17.blob.core.windows.net

Connections will fail with errors:

• ERR_CONNECTION_CLOSED
• ERR_EMPTY_RESPONSE

So problem occurs with any clients with Mihomo core below v1.9.12.

Working configurations

• Xray Core v25.8.31 + Mihomo < v1.9.12
• Latest Xray Core + Mihomo ≥ v1.9.13

The Mihomo upgrade workaround is not ideal as many users rely on older client versions and may not be able to upgrade immediately. This creates compatibility issues for existing deployments.

[kastov]

Debug logs from core.

[yuhan6665]

Need root cause otherwise if only break old mihomo would not qualify as a bug

[Fangliding]

其他客户端的实现一般不考虑 xray可以用的话没时间调查别的核心为什么不能用 更何况新版本都能用了/

[kastov]

@yuhan6665

The problem can be reproduced on own website using Nginx:

ssl_ecdh_curve prime256v1:secp384r1;

If this added – the problem occurs. (And it works fine from other client or newer version of Mihomo, or downgraded core Xray)

If added this, all is ok:

ssl_ecdh_curve X25519:prime256v1:secp384r1;

So it can be root cause of this issue.

[kastov]

@Fangliding @yuhan6665

I have made further investigations, this problem can occur not only with clients with old Mihomo cores, but with other applications as well.

The problem can be reproduced on Shadowrocket version 2.2.69 (2701) and below.
Seems like they fixed it only in 2.2.70 (2826), which was released to AppStore only 11 hours ago!