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

Advisory record · `GHSA-vp88-798v-h67f`

- **Identifiers:** `GHSA-vp88-798v-h67f` · `RUSTSEC-2026-0347`
- **State:** Confirmed
- **Severity:** CVSS 2.3 Low
- **Critical:** No
- **Weakness (CWE):** [CWE-200](https://cwe.mitre.org/data/definitions/200.html)
- **Tags:** [Information disclosure](https://agentprime.io/advisories/tag/info-disclosure.md)
- **Published:** 27 Oct 2026
- **Updated:** 27 Oct 2026
- **Reviewed by a person:** No

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.

## Affected packages

- `rustls` (crates.io): affected `>=0.23.44, <0.23.46 || >=0.24.0-dev.1, <0.24.0-dev.2`; fixed in `0.23.46`, `0.24.0-dev.2`

## 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

- 2.3 Low, CVSS 3.1: `CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N`, from GitHub Advisory Database

- **CISA KEV:** Not listed.
- **EPSS:** No score.

## Timeline

- 31 Oct 2026, 14:24 UTC: First seen by agentprime
- 31 Oct 2026, 14:24 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-vp88-798v-h67f)

## Sources

- [GitHub Advisory Database: GHSA-vp88-798v-h67f](https://github.com/advisories/GHSA-vp88-798v-h67f)
- [OSV: GHSA-vp88-798v-h67f](https://osv.dev/vulnerability/GHSA-vp88-798v-h67f)
- <https://github.com/rustls/rustls/security/advisories/GHSA-vp88-798v-h67f>
- <https://github.com/rustls/rustls/pull/3300>
- <https://github.com/rustls/rustls/pull/3354>
- <https://github.com/rustls/rustls/commit/2bd5c0cefabb2c5fd4100383a736d59f9671b9b4>
- <https://github.com/rustls/rustls/commit/4de14a508fbfa2273203ec17d9dfdd0fbd29e8d1>
- <https://github.com/rustls/rustls/commit/7dcbe4c1ae12185237d22e9197583329630a2014>
- <https://github.com/rustls/rustls>
- <https://github.com/rustls/rustls/releases/tag/v/0.23.46>
- <https://rustsec.org/advisories/RUSTSEC-2026-0347.html>

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.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-vp88-798v-h67f>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-vp88-798v-h67f/>. Everything for agents: <https://agentprime.io/llms.txt>.