CVE-2026-77528

Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation

Published Sep 18, 2026 CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed
Description
Autobahn Python is a WebSocket and WAMP implementation for Python that supports Twisted and asyncio. Prior to 26.7.1, WebSocket endpoints that accept permessage-deflate and rely on maxMessagePayloadSize enforce that limit against the compressed frame length before inflation but do not recheck the decompressed message size before delivery. A remote unauthenticated client can send a valid compressed frame below the configured wire-size limit that expands beyond the application message limit, causing oversized data to be allocated, joined, validated, and passed to application callbacks. This can create resource-exhaustion pressure, but the advisory does not establish confidentiality or integrity impact. This issue is fixed in version 26.7.1.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-hxp9-w8x3-p566 Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Crossbario
Crossbario autobahn-python
Vendors & Products Crossbario
Crossbario autobahn-python
Type Values Removed Values Added
Description Autobahn Python is a WebSocket and WAMP implementation for Python that supports Twisted and asyncio. Prior to 26.7.1, WebSocket endpoints that accept permessage-deflate and rely on maxMessagePayloadSize enforce that limit against the compressed frame length before inflation but do not recheck the decompressed message size before delivery. A remote unauthenticated client can send a valid compressed frame below the configured wire-size limit that expands beyond the application message limit, causing oversized data to be allocated, joined, validated, and passed to application callbacks. This can create resource-exhaustion pressure, but the advisory does not establish confidentiality or integrity impact. This issue is fixed in version 26.7.1.
Title Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation
Weaknesses CWE-409
CWE-770
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Sep 19, 2026, 2:11 PM
Reserved
Aug 20, 2026, 8:23 PM
Status
Deferred
Published
Sep 18, 2026, 8:17 PM
Modified
Sep 24, 2026, 9:25 PM