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CVE-2026-123611— rustls before 0.23.46 Key Exchange Downgrade via Unauthenticated ServerHello

Quick assessment

Affected
rustls rustls
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在版本 0.23.46 之前的 rustls 存在密钥交换降级漏洞。该漏洞允许网络攻击者通过未经认证的 ServerHello 消息，污染基于服务器名称的密钥交换组记录。攻击者可在一次连接中发送一个选择 X25519 算法的 ServerHello，导致后续客户端在 ClientHello 中仅发送经典（非抗量子）密钥份额，从而丧失后量子时代的机密性保障。

CVSS 3.7 · Low

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-123611

Vulnerability Information
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Vulnerability Title
rustls before 0.23.46 Key Exchange Downgrade via Unauthenticated ServerHello
Source: CVE Program / CVE List V5
Vulnerability Description
rustls before 0.23.46 contains a key exchange downgrade vulnerability that allows network attackers to poison the per-server-name key-exchange group record via an unauthenticated ServerHello. Attackers can answer one connection with a ServerHello selecting X25519, causing later ClientHellos to send only classical shares and lose post-quantum confidentiality.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在会话协商时选择低安全性的算法(算法降级)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
rustls rustls 0 ~ 0.23.46 -

II. Public POCs for CVE-2026-123611

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III. Intelligence Information for CVE-2026-123611

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Other References for CVE-2026-123611 (2)

Same Patch Batch · rustls · 2026-11-08 · 5 CVEs total

CVE-2026-123613 5.3 MEDIUM Rustls 0.23.13 before 0.23.45 TLS 1.3 Handshake Encryption Level Bypass
CVE-2026-123609 4.0 MEDIUM Rustls before 0.23.46 and 0.24.0-dev.1 before 0.24.0-dev.2 Secret Exposure via Debug
CVE-2026-123610 3.7 LOW rustls before 0.23.46 Denial of Service via Brotli Certificate Decompression
CVE-2026-123612 2.3 LOW rustls 0.23.44 and 0.23.45 ECH Rejection Application Data Disclosure

IV. Related Vulnerabilities

Same product: rustls
Same vendor: rustls
Same weakness: CWE-757