GHSA-hxp9-w8x3-p566: autobahn (CVE-2026-77528)

Package	Ecosystem	Affected	Fixed in
autobahn	PyPI	<26.7.1	26.7.1
crossbar	PyPI	<26.7.1	26.7.1

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Autobahn and Crossbar versions before 26.7.1 are affected. The message size limit (maxMessagePayloadSize) is checked against compressed WebSocket frame length, but not after permessage-deflate inflation, so a small compressed frame can expand into a larger message that reaches application handlers. A remote client that can connect to an endpoint accepting permessage-deflate can exploit this to exceed the configured limit, enabling resource exhaustion. Upgrade autobahn and crossbar to 26.7.1 or later.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
5.3	Medium	3.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.0052, the 44th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:09 UTC First seen by agentprime
31 Oct 2026, 14:09 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.