Vulnerability · Published Oct 26, 2026 · Assigned by GitHub_M

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

Medium 5.9

In plain English

A medium-severity resource allocation without limits in autobahn-python from crossbario. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 37% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium

Exploit odds (30 days)0.4%top 63.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
PyPI	autobahn	26.10.1	GHSA-pjh6-c8mg-3x7m
Ubuntu:22.04:LTS	python-autobahn	no fix listed	UBUNTU-CVE-2026-116579
Ubuntu:24.04:LTS	python-autobahn	no fix listed	UBUNTU-CVE-2026-116579
Ubuntu:26.04:LTS	python-autobahn	no fix listed	UBUNTU-CVE-2026-116579
Ubuntu:26.10	python-autobahn	no fix listed	UBUNTU-CVE-2026-116579

Affected products (as reported)

Vendor	Product	Versions
crossbario	autobahn-python	>= 26.7.1, < 26.10.1

Weakness: CWE-409, CWE-770 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References

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