---
id: GHSA-h2v8-394m-p7vv
aliases:
  - RUSTSEC-2026-0348
title: >-
  Rustls: Brotli certificate decompression can allocate an attacker-controlled
  amount of memory up to 1 GiB before authentication.
summary: >-
  Rustls: Brotli certificate decompression can allocate an attacker-controlled
  amount of memory up to 1 GiB before authentication.
severity: low
cvss: 3.7
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L'
vendor: rustls
product: rustls
ecosystem: rust
affected:
  - rustls < 0.23.46
  - 'rustls >= 0.24.0-dev.1, < 0.24.0-dev.2'
patched:
  - rustls 0.23.46
  - rustls 0.24.0-dev.2
published: '2026-10-27'
updated: '2026-10-27'
sourceUpdated: '2026-10-27T16:15:05.337819489Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-h2v8-394m-p7vv'
references:
  - url: 'https://github.com/rustls/rustls/security/advisories/GHSA-h2v8-394m-p7vv'
  - url: 'https://github.com/rustls/rustls/pull/3297'
  - url: 'https://github.com/rustls/rustls/pull/3354'
  - url: >-
      https://github.com/rustls/rustls/commit/1aa987af37d0d79b98781d345895ac0059ce345c
  - url: >-
      https://github.com/rustls/rustls/commit/402b7b78b7ae87d59e19cf07ee07f3fc19e6537e
  - url: 'https://github.com/rustls/rustls'
  - url: 'https://github.com/rustls/rustls/releases/tag/v/0.23.46'
  - url: 'https://rustsec.org/advisories/RUSTSEC-2026-0348.html'
  - url: 'https://github.com/advisories/GHSA-h2v8-394m-p7vv'
tags:
  - osv
  - rust
  - ghsa
cwe:
  - CWE-770
ingestedAt: '2026-10-27T16:11:58.700Z'
---

## Overview

### Summary

The built-in (but disabled by default) Brotli certificate decoder bounds the output buffer but accepts an input-selected history window. A header of five bytes can specify a 1 GiB window allocation. A peer can abort a process whose allocator cannot satisfy that request. A client must enable Brotli and connect to the peer; a server must enable Brotli and request a client certificate. Neither direction requires a trusted attacker certificate.

### Details

rustls calls `BrotliDecompress` which enables Brotli's large-window extension. rustls applies a limit to certificates, but this applies to the decompressed result, and not to any internal allocations the process requires.

### Impact

Client applications that enable the `brotli` feature will be vulnerable to malicious servers. Server applications that enable the `brotli` feature and enable client authentication will be vulnerable to malicious clients.

Potential for denial of service due to memory exhaustion from peers sending malicious Brotli-encoded certificates, for applications that enable Brotli decompression.

### Acknowledgement
Thanks to OpenAI [OutboundDisclosures@openai.com](mailto:OutboundDisclosures@openai.com) for the disclosure.

## Affected packages

- `rustls < 0.23.46`
- `rustls >= 0.24.0-dev.1, < 0.24.0-dev.2`

## Remediation

Upgrade to a patched release:

- `rustls 0.23.46`
- `rustls 0.24.0-dev.2`