Russh: Missing X25519 zero-point validation in hybrid ML-KEM key exchange

Exploitation

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

CVSS

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

EPSS

• CVE-2026-102824: 0.14% estimated exploitation activity in the next 30 days; percentile 3.47 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Vulnerability The hybrid ML-KEM 768 + X25519 key exchange implementation in russh/src/kex/hybridmlkem.rs does not validate that the remote peer's X25519 public key is not the zero point (all-zero 32-byte value). This allows a remote peer to force the X25519 contribution to the combined shared secret to zero, reducing the hybrid KEX to a single-algorithm exchange. Affected code at HEAD (v0.62.4, commit 0089c89): Server-side (serverdh, lines 92-93): Client-side (computesharedsecret, lines 154-155): Root Cause Commit a7fc1eb (2026-07-22, "fix mpint encoding and validate curve25519 keys") added zero-point validation to the standalone Curve25519 KEX in russh/src/kex/curve25519.rs at two locations: - serverdh line 77: if clientpubkey.0 == [0u8; 32] { return Err(crate::Error::Kex); } - computesharedsecret line 122: if remotepubkey.0 == [0u8; 32] { return Err(crate::Error::Kex); } The same X25519 scalar multiplication pattern appears in hybridmlkem.rs, but the fix was not applied there.…

Published by the source

30 Sep 2026, 23:26 UTC

Last modified by the source

30 Sep 2026, 23:30 UTC

Source last checked

26 Oct 2026, 15:43 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-w3jg-pjxf-73p4

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-w3jg-pjxf-73p4

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# Patch Next advisory brief: CVE-2026-102824

Advisory: Russh: Missing X25519 zero-point validation in hybrid ML-KEM key exchange
IDs: CVE-2026-102824, GHSA-w3jg-pjxf-73p4
Record: https://patchnext.com/advisories/cve-2026-102824 (revision 2, source checked 26 Oct 2026, 15:43 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: russh 0.63.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io russh: affected < 0.63.0; fixed in 0.63.0

## 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://osv.dev/vulnerability/GHSA-w3jg-pjxf-73p4 (OSV record GHSA-w3jg-pjxf-73p4 lists affected ranges: crates.io russh >=0 <0.63.0 (fixed))
- Verified: https://github.com/advisories/GHSA-w3jg-pjxf-73p4 (GitHub-reviewed advisory GHSA-w3jg-pjxf-73p4 lists affected ranges: crates.io russh >=0 <0.63.0)

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