CVE-2026-73430 Russh: Pre-auth remote panic via all-zero Curve25519 peer public value (encode_mpint OOB)
An unauthenticated attacker can cause a denial of service in the Russh SSH library by sending a malformed key exchange packet, crashing the server.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-73430?
CVE-2026-73430 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, an unauthenticated SSH client can cause a denial of service by sending SSH_MSG_KEX_ECDH_INIT with a 32-byte all-zero Q_C value. Curve25519Kex::server_dh in russh/src/kex/curve25519.rs accepts the all-zero peer public value and computes an all-zero shared secret, after which compute_exchange_hash calls encode_mpint in russh/src/kex/mod.rs and indexes beyond the end of the input while skipping leading zero bytes. The resulting panic occurs before authentication and terminates the server key-exchange task. This issue is fixed in version 0.62.4.
Weakness: CWE-754
Which versions are affected by CVE-2026-73430?
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-2026-73430?
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-2026-73430 being exploited?
There is no known exploitation of CVE-2026-73430 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-73430, GHSA-5xvq-cp9x-6p6r, UBUNTU-CVE-2026-73430.