# CVE-2026-128087: russh kex_done: shared-secret callback runs before server host-key verification

Status: published. Published: 2026-11-13. Updated: 2026-11-13.

russh is a Rust SSH client and server library that includes an SSH agent protocol implementation. From version 0.55.0 until version 0.65.1, the initial key exchange invokes client::Handler::kex_done() with the raw shared secret before check_server_key() accepts the server host key or certificate. A malicious SSH server can therefore trigger application-defined secondary-channel initialization or early data handling even when the server identity is subsequently rejected. Ordinary clients that keep the callback's no-op default or independently defer callback-derived actions until trust is confirmed are not affected. This issue is fixed in version 0.65.1.

## Remediation

- fix: russh (crates.io): OSV reports a fixed version 0.65.1. Check the advisory for supported release branches. (source: OSV GHSA-9264-jvgf-6w2f) — https://github.com/advisories/GHSA-9264-jvgf-6w2f

## Affected products and versions

- Eugeny / russh: >= 0.55.0, < 0.65.1 (affected). Source: CNA: GitHub_M
-  / russh (russh): ≥ 0.55.0; < 0.65.1 (affected, semver); OSV events: introduced 0.55.0; fixed 0.65.1. Source: OSV GHSA-9264-jvgf-6w2f

## Severity and prioritization

- CVSS 3.1: 3.7 (low); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: exploitation poc; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-696, CWE-863

## Exploit evidence

- exploit: https://github.com/Eugeny/russh/security/advisories/GHSA-9264-jvgf-6w2f (ADP: CISA-ADP)

## References

- https://github.com/Eugeny/russh/security/advisories/GHSA-9264-jvgf-6w2f (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/Eugeny/russh/pull/808 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/Eugeny/russh/commit/43a46d67a80a7355fcd2fb25e7e00d79aec8184c (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/Eugeny/russh/releases/tag/v0.65.1 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/Eugeny/russh/security/advisories/GHSA-9264-jvgf-6w2f (ADP: CISA-ADP; exploit)

- https://github.com/advisories/GHSA-9264-jvgf-6w2f (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-9264-jvgf-6w2f (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-128087; retrieved 2026-11-13; source updated 2026-11-13

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-9264-jvgf-6w2f; retrieved 2026-11-13; source updated 2026-11-13

Revision: 8659efc4b8d55fcb15d970fb7bf40328962ba2d366f5f077b806b3374f411371

Canonical: https://y2.dev/cve/CVE-2026-128087

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