CVE-2026-73429 Russh: client wrong-length X25519 `clone_from_slice` panic (pre-auth DoS)
A malicious SSH server can crash a russh client session by sending a malformed key exchange reply, causing a panic before host key verification.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-73429?
CVE-2026-73429 is a medium-severity denial of service vulnerability in Eugeny russh, published on 12 Aug 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 0.62.4, a malicious SSH server can crash a russh client session with a malformed KEX_ECDH_REPLY containing a server ephemeral value that is not 32 bytes long. The client-side Curve25519Kex::compute_shared_secret function in russh/src/kex/curve25519.rs passes the decoded exchange.server_ephemeral value to clone_from_slice without validating its length, causing a deterministic panic before the server host key is verified. The panic terminates the spawned client session task and surfaces as a JoinError, while the embedding process normally remains running. This issue is fixed in version 0.62.4.
Which versions are affected by CVE-2026-73429?
2 open source packages ship an affected version, including russh.
| Package | Affected | Fixed in |
|---|---|---|
russh crates.io | All versions | 0.62.4 |
russh crates.io | All versions | 0.62.4 |
How do I fix CVE-2026-73429?
Upgrade russh to 0.62.4 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-2026-73429 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73429 exists.
Sources
Also known as DEBIAN-CVE-2026-73429, GHSA-g9hv-x236-4qp3, UBUNTU-CVE-2026-73429.