Vulnerability · Published Sep 18, 2026 · Assigned by GitHub_M
CVE-2026-77528Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation
Medium 5.3
In plain English
A medium-severity resource allocation without limits in autobahn-python from crossbario. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | python-autobahn | no fix listed | DEBIAN-CVE-2026-77528 |
| Debian:13 | python-autobahn | no fix listed | DEBIAN-CVE-2026-77528 |
| Debian:14 | python-autobahn | no fix listed | DEBIAN-CVE-2026-77528 |
| PyPI | autobahn | 26.7.1 | PYSEC-2026-4027 |
| PyPI | autobahn | 26.7.1 | GHSA-hxp9-w8x3-p566 |
| PyPI | crossbar | 26.7.1 | GHSA-hxp9-w8x3-p566 |
| PyPI | crossbar | 26.7.1 | PYSEC-2026-4031 |
| Ubuntu:22.04:LTS | python-autobahn | no fix listed | UBUNTU-CVE-2026-77528 |
| Ubuntu:24.04:LTS | python-autobahn | no fix listed | UBUNTU-CVE-2026-77528 |
| Ubuntu:26.04:LTS | python-autobahn | no fix listed | UBUNTU-CVE-2026-77528 |
| Ubuntu:26.10 | python-autobahn | no fix listed | UBUNTU-CVE-2026-77528 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| crossbario | autobahn-python | < 26.7.1 |
Weakness: CWE-409, CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
References
- https://github.com/crossbario/autobahn-python/security/advisories/GHSA-hxp9-w8x3-p566 x_refsource_CONFIRM
- https://github.com/crossbario/autobahn-python/pull/1916 x_refsource_MISC
- https://github.com/crossbario/autobahn-python/commit/77d323a30b09b1828ad8be2ce6344e056970e613 x_refsource_MISC
- https://github.com/crossbario/autobahn-python/releases/tag/v26_7_1 x_refsource_MISC