RUSTSEC-2026-0349: Unauthenticated ServerHello can downgrade later connections to classical key exchange

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难度
4/5
预计耗时
3-5 天
新手友好度
35/100
Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
活跃
技术栈
rust
领域
security

调研方向

The report identifies the affected dependency as rustls 0.23.45 and links rustls pull request 3355; it does not name files or tests in sentry-rust. Start by checking how this SDK pins and configures rustls, then review the linked fix and advisory details. Done means the affected dependency behavior is addressed and relevant checks confirm the fix.

由索引模型根据 Issue 内容生成。

描述

Rust

Unauthenticated ServerHello can downgrade later connections to classical key exchange

Details
Package rustls
Version 0.23.45
URL https://github.com/rustls/rustls/pull/3355
Date 2026-10-14
Patched versions >=0.23.46

The client recorded the server-selected key exchange group for each server
name when processing the ServerHello, before the server was authenticated.
This record is used to predict which key share to send in future ClientHellos
to that server name.

A network attacker can answer one connection attempt with a ServerHello
selecting X25519, and then close the connection. Later ClientHellos for that
name carry only an X25519 key share, while supported_groups still lists
X25519MLKEM768 first. If the genuine server accepts that share rather than
sending a HelloRetryRequest for its preferred hybrid group, the handshake
completes with classical-only key exchange and no error. This persists for as
long as the entry stays in the client's session store.

The impact is loss of post-quantum confidentiality for affected connections
("harvest now, decrypt later"). There is no key compromise and no
authentication bypass.

The following are not affected:

  • connections to servers which send a HelloRetryRequest for their preferred group,
  • clients with resumption disabled (as nothing is stored), and
  • other server names.

This behaviour is discussed in
draft-ietf-tls-key-share-prediction,
so the practical impact depends largely on server policy.

See advisory page for additional details.

主要语言
Rust
星标
755
派生
192
平均合并
3 天 15 小时
30 天内合并 PR
12

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  • 没有 Dockerfile 或 Docker Compose 文件
  • 有 Pull Request 模板
  • 没有贡献指南

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  3. Fork 仓库,在一个分支上完成修改。
  4. 提交 Pull Request,并在描述里引用这个 Issue 编号。

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