---
id: "CVE-2026-123611"
page: "https://infrastack.ai/live/CVE-2026-123611"
kind: "vulnerability"
aliases: ["CVE-2026-123611"]
title: "rustls: forged ServerHello can strip post-quantum key exchange from later connections"
severity: "medium"
cvss: 6.3
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["package", "post-quantum", "rust", "rustls", "tls"]
not_affected_if: ["no-post-quantum-kx", "tls-server-only"]
published_at: "2026-11-08T02:16:56+00:00"
first_seen_at: "2026-11-08T02:21:14+00:00"
updated_at: "2026-11-08T02:24:52+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123611", "first_seen_at": "2026-11-08T02:21:14+00:00"}]
exploit_sources: []
---

# rustls: forged ServerHello can strip post-quantum key exchange from later connections

Link for people: https://infrastack.ai/live/CVE-2026-123611 (this .md is for agents)

rustls is a TLS library for Rust programs. A network attacker can answer one connection with a forged ServerHello that selects X25519, which makes rustls remember a classical-only key exchange for that server name and send only classical key shares on later connections, losing post-quantum confidentiality.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Find rustls in the Cargo.lock file of each Rust project, for example `grep -A1 'name = "rustls"' Cargo.lock`
- Check the rustls version listed against the fixed version below

## Fix

- rustls: upgrade to `0.23.46` or later

## Timeline

- 2026-11-08T02:21:14+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123611

## Documents

- [advisory] Vendor advisory: github.com https://github.com/rustls/rustls/security/advisories/GHSA-w44r-93j7-qv28
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/rustls-before-0.23.46-key-exchange-downgrade-via-unauthenticated-serverhello

## From the sources

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.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_