Autobahn Python is a WebSocket and WAMP implementation for Python that supports Twisted and asyncio.
CVE-2026-116579
Summary permessage-brotli inflates each frame fully before checking maxMessagePayloadSize, so one 421-byte frame makes the server allocate about 545 MiB even with a 1 MiB message limit (brotli expands about 1,000,000:1). Any unauthenticated client can exhaust server memory this way on servers that enable permessage-brotli. This bypasses the GHSA-hxp9-w8x3-p566 fix. Details In 26.7.1 the receive path passes the remaining maxMessagePayloadSize budget to decompressmessagedata(..., maxoutputlen=...). deflate and bzip2 stop at that budget. PerMessageBrotli.decompressmessagedata (compressbrotli.py) instead calls self.decompressor.process(data) with no limit and compares the length afterwards, so the whole frame is inflated first. The code comment and changelog say this is still "bounded on the wire by maxFramePayloadSize", but brotli reaches about 1,000,000:1 (841 bytes inflate to 1 GiB), so that bound means little. A 421-byte frame against a 1 MiB budget peaks at 545 MiB before the 1009 rejection. An autobahn asyncio server on 127.0.0.1 accepting permessage-brotli, with maxFramePayloadSize=64 KiB and maxMessagePayloadSize=1 MiB, received one small brotli frame from an autobahn client…
Assessment
- CVSS
- 5.9 (v3.1)
- Severity
- Medium
- EPSS
- 0.00425% chance of exploitation in the next 30 days
- Known exploited
- Not listed in CISA KEV
- Exploit availability
- Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
- Published
- 26 October 2026
- Last updated
- 28 October 2026
- Affected
- pip · autobahn
- Weakness
- CWE-409, CWE-770
- Assigner
- security-advisories@github.com
CVSS vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
At the source
References
- https://github.com/crossbario/autobahn-python/commit/a41442bbee4f6126a8ce1bb892840124c24d16f1
- https://github.com/crossbario/autobahn-python/pull/1987
- https://github.com/crossbario/autobahn-python/releases/tag/v26_10_1
- https://github.com/crossbario/autobahn-python/security/advisories/GHSA-pjh6-c8mg-3x7m
- https://nvd.nist.gov/vuln/detail/CVE-2026-116579
- https://github.com/advisories/GHSA-pjh6-c8mg-3x7m
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