CVE-2026-102821 Russh: Unbounded memory exhaustion via CHANNEL_OPEN flood during a client-stalled rekey
An authenticated remote peer can cause memory exhaustion and crash the server by flooding channel open messages during a stalled key exchange.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-102821?
CVE-2026-102821 is a medium-severity denial of service vulnerability in Eugeny russh, published on 29 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
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.
Which versions are affected by CVE-2026-102821?
2 open source packages ship an affected version, including russh.
| Package | Affected | Fixed in |
|---|---|---|
russh crates.io | All versions | 0.63.2 |
russh crates.io | All versions | 0.63.2 |
How do I fix CVE-2026-102821?
Upgrade russh to 0.63.2 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-102821 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-102821 exists.
Sources
Also known as DEBIAN-CVE-2026-102821, GHSA-35g8-35p8-c8fw, UBUNTU-CVE-2026-102821.