UBUNTU-CVE-2026-123611: Medium severity ubuntu/rust-rustls vulnerability
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.
Affected Software
Event History
Frequently Asked Questions
What must an attacker be able to do to exploit this issue?
The attacker must be able to act as a network attacker and send an unauthenticated ServerHello for a connection. Exploitation has high attack complexity and does not require privileges or user interaction.
What is the impact after a successful downgrade?
The attacker can cause later ClientHellos for the affected server name to offer only classical key shares. This removes post-quantum confidentiality for those later connections, while the stated impact is limited to confidentiality.
Which versions are affected?
rustls versions before 0.23.46 are affected. The listed Ubuntu package is ubuntu/rust-rustls.