What’s Vulnerable › Vulnerabilities

CVE-2026-77528: Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-18 · updated 2026-09-24
• Weakness: CWE-409

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.

Affected products

• crossbario autobahn-python: before 26.7.1

References

• https://github.com/crossbario/autobahn-python/commit/77d323a30b09b1828ad8be2ce6344e056970e613
• https://github.com/crossbario/autobahn-python/pull/1916
• https://github.com/crossbario/autobahn-python/releases/tag/v26_7_1
• https://github.com/crossbario/autobahn-python/security/advisories/GHSA-hxp9-w8x3-p566

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