CVE-2026-42189 Russh: Pre-auth DoS via unbounded allocation in keyboard-interactive auth
A malicious client can crash russh-based SSH servers via unbounded allocation in keyboard-interactive authentication without credentials.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42189?
CVE-2026-42189 is a high-severity denial of service vulnerability in Eugeny russh, published on 8 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Russh is a Rust SSH client & server library. Prior to version 0.60.1, a pre-authentication denial-of-service vulnerability exists in the server's keyboard-interactive authentication handler. A malicious client can crash any russh-based server that implements keyboard-interactive auth (e.g., for 2FA/TOTP) with a single malformed packet, requiring no credentials. This issue has been patched in version 0.60.1.
Which versions are affected by CVE-2026-42189?
2 open source packages ship an affected version, including russh. It affects 2 products.
| Package | Affected | Fixed in |
|---|---|---|
russh crates.io | All versions | 0.60.1 |
russh crates.io | All versions | 0.60.1 |
Products include Russh Project Russh, Warpgate Project Warpgate.
How do I fix CVE-2026-42189?
Upgrade russh to 0.60.1 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-2026-42189 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42189 exists.
Other vulnerabilities in Eugeny russh
Sources
Also known as DEBIAN-CVE-2026-42189, GHSA-f5v4-2wr6-hqmg, UBUNTU-CVE-2026-42189.