Russh: Unbounded memory exhaustion via CHANNEL_OPEN flood during a client-stalled rekey

[ Why it matters ]Priority signals

• Public proof-of-concept exploit exists (CISA SSVC)

[ Description ]Official description

Russh is a Rust SSH client and server library. Prior to 0.63.2, an authenticated remote peer can send SSH_MSG_KEXINIT without the required SSH_MSG_KEX_ECDH_INIT and then flood SSH_MSG_CHANNEL_OPEN messages while SessionKexState::InProgress prevents priority_receiver in russh/src/server/session.rs from being drained. The server continues processing network input and enqueues a ChannelOpenReply for each request on an unbounded channel, allowing one connection to grow memory until the process is terminated. This issue is fixed in version 0.63.2.

[ Fixes ]Fixes and patches

• russh 0.63.2Fixed version · GitHub Advisories · rust package russh: upgrade to 0.63.2 or later (affected <= 0.63.1)

[ Packages ]Affected open-source packages

• russh rustAffected <= 0.63.1 · fixed in 0.63.2 · GHSA-35g8-35p8-c8fw

[ References ]References

• github.com/Eugeny/russh/commit/a282af361ac99bc76b80876d1aae128e89dbf66b
• github.com/Eugeny/russh/releases/tag/v0.63.2
• github.com/Eugeny/russh/security/advisories/GHSA-35g8-35p8-c8fw