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Advisory record · GHSA-vp88-798v-h67f

rustls: ECH rejection can expose buffered application data to authenticated outer server before `ech_required` alert

CVSS 2.3 Low

Published by the GitHub Advisory Database at 27 Oct 2026, 16:08 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
rustlscrates.io>=0.23.44, <0.23.46 || >=0.24.0-dev.1, <0.24.0-dev.20.23.46, 0.24.0-dev.2
Identifiers
GHSA-vp88-798v-h67f · RUSTSEC-2026-0347
Weakness (CWE)
CWE-200
Tags
Published
27 Oct 2026
Updated
27 Oct 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Versions 0.23.44 and 0.23.45 of rustls, and 0.24.0-dev.1 of rustls, are affected. When a server rejects Encrypted Client Hello, data a client wrote before the handshake completed is sent to the outer server named by public_name before the ech_required alert, which violates RFC 9849. The attacker needs no special access, since the exposed server is authenticated; the risk applies to clients using EchMode::Enable that write data early and hit a rejection, such as with a stale config. Upgrade to rustls 0.23.46 or 0.24.0-dev.2.

Written 3 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
2.3 Low 3.1 CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N GitHub Advisory Database
  • CISA KEV Not listed.
  • EPSS No score.

Timeline

  1. 31 Oct 2026, 14:24 UTC First seen by agentprime
  2. 31 Oct 2026, 14:24 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.