CVE-2026-116579

MEDIUM 5.9

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

CVSS Score

5.9

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-409 CWE-770
Vendor	crossbario
Product	autobahn-python
Published	Oct 26, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Affected Versions

crossbario / autobahn-python

>= 26.7.1, < 26.10.1

References

NVD ↗ CVE.org ↗ EPSS Data ↗

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