CVE-2026-123611: Security vulnerability

Published Nov 8, 2026

Updated

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.

Event History

Nov 8, 2026

CVE Published

via NVD·02:16 AM

Data Sourced

via NVD·02:16 AM

DescriptionSeverityWeakness

Frequently Asked Questions

Who is exposed to this downgrade?

Clients using rustls before 0.23.46 are exposed when a network attacker can intercept or respond to a connection for a target server name. The issue affects the client-side per-server-name key-exchange group record.

What must an attacker do to exploit the issue?

The attacker must be able to send an unauthenticated ServerHello for one connection and select X25519. This poisons the stored record so later ClientHellos for that server name send only classical key shares.

What is the security impact after the record is poisoned?

Later connections to the affected server name lose post-quantum confidentiality because their ClientHellos contain only classical shares.

How can this be remediated?

Update rustls to version 0.23.46 or later. The provided information does not identify a workaround for installations that cannot immediately update.

CVE-2026-123611: Security vulnerability

Event History

Frequently Asked Questions

Who is exposed to this downgrade?

What must an attacker do to exploit the issue?

What is the security impact after the record is poisoned?

How can this be remediated?

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Frequently Asked Questions

Who is exposed to this downgrade?

What must an attacker do to exploit the issue?

What is the security impact after the record is poisoned?

How can this be remediated?