russh kex_done: Shared-secret callback runs before server host-key verification

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

3.7 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2026-128087: 0.24% estimated exploitation activity in the next 30 days; percentile 15.05 (FIRST EPSS, 2026-11-14). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A malicious SSH server whose host key is rejected can still cause russh's `client::Handler::kex_done()` callback to execute with the raw key-exchange shared secret. Applications using the callback for its documented protocol-bridging purpose may derive keys, initialize a secondary data channel, or perform another externally visible action before russh calls `check_server_key()` and rejects the server.

Details During the initial key exchange, russh calls `kex_done()` immediately after the server proves possession of the presented host key, but before the application decides whether that key belongs to the intended server: ```rust let shared_secret = newkeys.kex.shared_secret_bytes(); handler .kex_done(shared_secret, &newkeys.names, session) .await?; // Initial KEX only checks trust afterwards. if let Some(certificate) = server_host_certificate { if !handler.check_server_key(&certificate.into()).await? { return Err(crate::Error::UnknownKey.into()); } } else if let…

Published by the source

13 Nov 2026, 19:20 UTC

Last modified by the source

13 Nov 2026, 19:30 UTC

Source last checked

14 Nov 2026, 08:25 UTC

1. Revision 2 · amended · 14 Nov 2026

   Amended from osv record GHSA-9264-jvgf-6w2f

2. Revision 1 · created · 13 Nov 2026

   Published from ghsa record GHSA-9264-jvgf-6w2f

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# Patch Next advisory brief: CVE-2026-128087

Advisory: russh kex_done: Shared-secret callback runs before server host-key verification
IDs: CVE-2026-128087, GHSA-9264-jvgf-6w2f
Record: https://patchnext.com/advisories/cve-2026-128087 (revision 2, source checked 14 Nov 2026, 08:25 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: russh 0.65.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io russh: affected >= 0.55.0, < 0.65.1; fixed in 0.65.1

## Suggested inspection (read-only)
- crates.io russh: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on russh.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9264-jvgf-6w2f (GitHub-reviewed advisory GHSA-9264-jvgf-6w2f lists affected ranges: crates.io russh >=0.55.0 <0.65.1)
- Verified: https://osv.dev/vulnerability/GHSA-9264-jvgf-6w2f (OSV record GHSA-9264-jvgf-6w2f lists affected ranges: crates.io russh >=0.55.0 <0.65.1 (fixed))

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