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Low, CVSS 3.7amended

rustls: An unauthenticated ServerHello poisons the per-name key-exchange record, so later ClientHellos carry only a classical X25519 share

GHSA-w44r-93j7-qv28

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (rustls 0.24.0-dev.2, 0.23.46), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • crates.io rustls

    Affected
    < 0.23.46>= 0.24.0-dev.1, < 0.24.0-dev.2
    Fixed in
    0.24.0-dev.2, 0.23.46

Sources

Severity and exploitation
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
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

Summary The client records the server-selected key-exchange group per server name when it processes the ServerHello, before the server is authenticated. A network attacker can answer one connection attempt for a target name with a ServerHello that selects X25519 and close the connection. Later ClientHellos for that name carry one X25519 share while supported_groups still lists X25519MLKEM768 first. If the server accepts that share instead of sending a HelloRetryRequest, the handshake completes with classical key exchange only and no error. An attacker that answers one connection attempt for the target name with a ServerHello selecting X25519 changes every later ClientHello of that client for that name, for as long as the entry stays in the store. No certificate or completed handshake is needed: it parses the ClientHello, sends the ServerHello, and closes. TLS 1.3 transcript binding stops an on-path attacker from editing the ClientHello of one connection. It does not stop the…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from osv record GHSA-w44r-93j7-qv28

  2. Revision 2 · amended ·

    Amended from ghsa record GHSA-w44r-93j7-qv28

  3. Revision 1 · created ·

    Published from osv record RUSTSEC-2026-0349

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: GHSA-w44r-93j7-qv28

Advisory: rustls: An unauthenticated ServerHello poisons the per-name key-exchange record, so later ClientHellos carry only a classical X25519 share
IDs: GHSA-w44r-93j7-qv28
Record: https://patchnext.com/advisories/rustsec-2026-0349 (revision 3, source checked 28 Oct 2026, 06:30 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: rustls 0.24.0-dev.2, 0.23.46. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io rustls: affected < 0.23.46; >= 0.24.0-dev.1, < 0.24.0-dev.2; fixed in 0.24.0-dev.2, 0.23.46

## Suggested inspection (read-only)
- crates.io rustls: 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 rustls.
- 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/RUSTSEC-2026-0349 (OSV record RUSTSEC-2026-0349 lists affected ranges: crates.io rustls >=0.0.0-0 <0.23.46 (fixed))
- Verified: https://github.com/advisories/GHSA-w44r-93j7-qv28 (GitHub-reviewed advisory GHSA-w44r-93j7-qv28 lists affected ranges: crates.io rustls >=0 =0.24.0-dev.1 <0.24.0-dev.2)
- Verified: https://osv.dev/vulnerability/GHSA-w44r-93j7-qv28 (OSV record GHSA-w44r-93j7-qv28 lists affected ranges: crates.io rustls >=0 =0.24.0-dev.1 <0.24.0-dev.2 (fixed))

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