---
id: CVE-2026-116579
title: >-
  Autobahn Python: permessage-brotli inflates a whole frame before
  maxMessagePayloadSize is checked (incomplete fix of GHSA-hxp9-w8x3-p566)
summary: >-
  Autobahn Python is a WebSocket and WAMP implementation for Python that
  supports Twisted and asyncio. From 26.7.1 until 26.10.1,
  PerMessageBrotli.decompress_message_data in compress_brotli.py calls the
  Brotli decompressor without an outpu…
severity: medium
cvss: 5.9
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
cwe:
  - CWE-409
  - CWE-770
vendor: crossbario
product: autobahn-python
affected:
  - 'autobahn-python >= 26.7.1, < 26.10.1'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-27T13:41:50.957164Z'
published: '2026-10-26'
updated: '2026-10-27'
sourceUpdated: '2026-10-27T14:18:18.772Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-116579'
references:
  - url: >-
      https://github.com/crossbario/autobahn-python/security/advisories/GHSA-pjh6-c8mg-3x7m
    label: >-
      https://github.com/crossbario/autobahn-python/security/advisories/GHSA-pjh6-c8mg-3x7m
  - url: 'https://github.com/crossbario/autobahn-python/pull/1987'
    label: 'https://github.com/crossbario/autobahn-python/pull/1987'
  - url: >-
      https://github.com/crossbario/autobahn-python/commit/a41442bbee4f6126a8ce1bb892840124c24d16f1
    label: >-
      https://github.com/crossbario/autobahn-python/commit/a41442bbee4f6126a8ce1bb892840124c24d16f1
  - url: 'https://github.com/crossbario/autobahn-python/releases/tag/v26_10_1'
    label: 'https://github.com/crossbario/autobahn-python/releases/tag/v26_10_1'
tags:
  - cve.org
epss: 0.00425
epssPercentile: 0.36588
ingestedAt: '2026-10-26T20:39:42.614Z'
---

## Overview

Autobahn Python is a WebSocket and WAMP implementation for Python that supports Twisted and asyncio. From 26.7.1 until 26.10.1, PerMessageBrotli.decompress_message_data in compress_brotli.py calls the Brotli decompressor without an output limit and checks maxMessagePayloadSize only after a complete frame has been inflated. An unauthenticated WebSocket client can send a small, highly compressed frame that allocates hundreds of MiB before rejection, causing memory-exhaustion denial of service on servers that enable the opt-in permessage-brotli feature through the compress extra. Deflate and bzip2 already enforce the remaining output budget and are outside this residual vulnerability. This issue is fixed in version 26.10.1.

## Affected

- `autobahn-python >= 26.7.1, < 26.10.1`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.