# CVE-2026-73429: Russh SSH library Curve25519 key exchange denial of service

Source: https://junglewise.ai/threats/cve-2026-73429-russh-ssh-library-curve25519-key-exchange-denial-of-service  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-12. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-73429 · Severity: medium · CVSS 5.3 · Published 2026-08-12

Russh is a Rust library that implements SSH client and server functionality, widely used in applications that need to communicate securely over SSH. A malicious SSH server can send a malformed key exchange packet that causes a Russh client to crash and terminate its session, resulting in a denial of service. This prevents legitimate users from completing their SSH connection, though the wider application typically remains operational.

Technologies: [russh (crates.io)](https://junglewise.ai/threats/technologies/crates-io-russh). Vendors: [crates.io](https://junglewise.ai/threats/vendors/crates-io).

## Quick answers

**Is CVE-2026-73429 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-73429 being exploited in the wild.

**How severe is CVE-2026-73429?** Medium severity, with a CVSS score of 5.3, published 12 August 2026.

**Which products and versions are affected?** russh (crates.io) SEMVER:introduced=0,fixed=0.62.4.

**Is there a fix for CVE-2026-73429?** Yes. russh (crates.io): upgrade to 0.62.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-73429 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-73429?** Check whether you run russh (crates.io) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- russh (crates.io): upgrade to 0.62.4 or later

  ```sh
  cargo update -p russh
  ```


## Technical details

The vulnerability is a denial-of-service condition in the Curve25519 key exchange implementation. When processing a KEX_ECDH_REPLY message, the client-side Curve25519Kex::compute_shared_secret function in russh/src/kex/curve25519.rs fails to validate the length of the server's ephemeral public key before calling clone_from_slice, causing a panic if the key is not exactly 32 bytes. This panic occurs before the server's host key is verified, allowing an unauthenticated attacker to crash client sessions. Attack vector is network-based and requires no authentication; a malicious or compromised SSH server can trigger the crash. The issue is fixed in version 0.62.4 by validating key lengths.

## Affected products

- Eugeny Russh prior to 0.62.4

## Identifiers

- CVE-2026-73429
- GHSA-g9hv-x236-4qp3

## Timeline

- 2026-08-12: disclosed
- 2026-07-22: patched: Version 0.62.4 released with security fix

## References

- [https://github.com/Eugeny/russh/commit/a7fc1eb5717264e31c3c5f7dd849b73989a08f3d](https://github.com/Eugeny/russh/commit/a7fc1eb5717264e31c3c5f7dd849b73989a08f3d)
- [https://github.com/Eugeny/russh/releases/tag/v0.62.4](https://github.com/Eugeny/russh/releases/tag/v0.62.4)

## Related threats

- [russh SSH server signature algorithm mismatch in publickey auth](https://junglewise.ai/threats/cve-2026-111062-a-russh-ssh-server-accepts-a-publickey-authentication-whose)
- [russh SSH agent confirmation bypass](https://junglewise.ai/threats/cve-2026-116794-russh-is-a-rust-ssh-client-and-server-library-that-includes-an)
- [russh SSH library zero maximum packet size denial of service](https://junglewise.ai/threats/cve-2026-116774-russh-is-a-rust-ssh-client-and-server-library-that-includes-an)
- [russh memory exhaustion via unbounded EXT_INFO packets](https://junglewise.ai/threats/cve-2026-116773-russh-is-a-rust-ssh-client-and-server-library-that-includes-an)
- [russh's SSH agent server is susceptible to unbound allocations via repeated SSH_AGENT_CONSTRAIN_CONFIRM messages](https://junglewise.ai/threats/cve-2026-116696-russh-is-a-rust-ssh-client-and-server-library-that-includes-an)