Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-77528
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-18 20:17:22 UTC
Updated2026-09-24 21:25:27 UTC
DescriptionAutobahn 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.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

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

EPSS: 0.005240000 probability, percentile 0.420040000 (date 2026-09-25)

Problem Types: CWE-409 | CWE-770 | CWE-409 CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) | CWE-770 CWE-770: Allocation of Resources Without Limits or Throttling

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
3.1CNADECLARED5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Crossbario Autobahn-python affected < 26.7.1 Not specified

References

ReferenceSourceLinkTags
github.com/crossbario/autobahn-python/security/advisories/GHSA-hxp9-w8x3... [email protected] github.com
github.com/crossbario/autobahn-python/releases/tag/v26_7_1 [email protected] github.com
github.com/crossbario/autobahn-python/commit/77d323a30b09b1828ad8be2ce63... [email protected] github.com
github.com/crossbario/autobahn-python/pull/1916 [email protected] github.com
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