{"id":"CVE-2026-116579","kind":"vulnerability","aliases":["CVE-2026-116579"],"related":[],"title":"Autobahn Python: crafted Brotli WebSocket frame exhausts server memory","description":"Autobahn Python is a WebSocket and WAMP implementation for Python that supports Twisted and asyncio. From 26.7.1 until 26.10.1, PerMessageBrotli.decompress_message_data in compress_brotli.py calls the Brotli decompressor without an output limit and checks maxMessagePayloadSize only after a complete frame has been inflated. An unauthenticated WebSocket client can send a small, highly compressed frame that allocates hundreds of MiB before rejection, causing memory-exhaustion denial of service on servers that enable the opt-in permessage-brotli feature through the compress extra. Deflate and bzip2 already enforce the remaining output budget and are outside this residual vulnerability. This issue is fixed in version 26.10.1.","summary":"Autobahn Python's permessage-brotli decompression runs without an output limit, so a small compressed WebSocket frame can allocate hundreds of MiB before the payload size check rejects it. An unauthenticated client can use this to cause memory-exhaustion denial of service.","severity":"medium","cvss":5.9,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["autobahn","package","python","self-hosted","websocket"],"not_affected_if":["default-config","pre-26.7.1-or-post-26.10.1"],"how_to_check":"- Run `pip show autobahn` and check whether the installed version is between `26.7.1` and `26.10.1`.\n- Check whether the `compress` extra is installed and the permessage-brotli feature is enabled in the WebSocket server configuration (unknown if the sources give the exact setting name).","fix":"- Upgrade the autobahn package to `26.10.1` or later.","status":"open","published_at":"2026-10-26T21:18:15+00:00","first_seen_at":"2026-10-26T21:20:31+00:00","triaged_at":"2026-10-26T21:21:13+00:00","updated_at":"2026-10-26T21:21:13+00:00","category":"package","confidence":0.8,"triage":{"at":"2026-10-26T21:21:13Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade the autobahn package to `26.10.1` or later.","reach":"internet","title":"Autobahn Python: crafted Brotli WebSocket frame exhausts server memory","impact":"medium","summary":"Autobahn Python's permessage-brotli decompression runs without an output limit, so a small compressed WebSocket frame can allocate hundreds of MiB before the payload size check rejects it. An unauthenticated client can use this to cause memory-exhaustion denial of service.","category":"package","nicknames":[],"who_cares":["python","autobahn","websocket","self-hosted"],"confidence":0.8,"needs_auth":"no","worst_case":"Unauthenticated clients exhaust server memory, causing denial of service.","analyst_note":"","how_to_check":"- Run `pip show autobahn` and check whether the installed version is between `26.7.1` and `26.10.1`.\n- Check whether the `compress` extra is installed and the permessage-brotli feature is enabled in the WebSocket server configuration (unknown if the sources give the exact setting name).","needs_analyst":false,"not_affected_if":["default-config","pre-26.7.1-or-post-26.10.1"],"who_is_affected":"Servers running Autobahn Python from `26.7.1` up to but not including `26.10.1` that enable the opt-in permessage-brotli feature through the compress extra. Deflate and bzip2 compression are not part of this issue. Deployments on other versions, or without permessage-brotli enabled, can skip it.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"medium"},"cost_usd":0.000628,"input_tokens":3473,"output_tokens":561,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-116579':12A,15A '-2026':11A,14A '26.10.1':85C,172C '26.7.1':83C 'alloc':42B,122C 'alreadi':154C 'asyncio':81C 'autobahn':1A,16B,23B,67C 'brot':4A,28B,93C,145C 'budget':159C 'bzip2':153C 'call':91C 'caus':60B,128C 'check':50B,100C 'client':55B,113C 'complet':105C 'compress':38B,119C,149C 'compress_brotli.py':90C 'craft':3A 'cve':10A,13A 'data':88C 'decompress':29B 'decompressor':94C 'deflat':151C 'denial':64B,132C 'enabl':138C 'enforc':155C 'exhaust':7A,63B,131C 'extra':150C 'featur':146C 'fix':169C 'frame':6A,40B,106C,120C 'high':118C 'host':21B 'hundr':43B,123C 'implement':74C 'inflat':109C 'issu':167C 'limit':34B,98C 'maxmessagepayloads':101C 'memori':9A,62B,130C 'memory-exhaust':61B,129C 'messag':87C 'mib':45B,125C 'opt':141C 'opt-in':140C 'output':33B,97C,158C 'outsid':162C 'packag':17B 'payload':48B 'permessag':27B,144C 'permessage-brot':26B,143C 'permessagebrotli.decompress':86C 'python':2A,18B,24B,68C,76C 'reject':51B,127C 'remain':157C 'residu':164C 'run':30B 'self':20B 'self-host':19B 'send':115C 'server':8A,136C 'servic':66B,134C 'size':49B 'small':37B,117C 'support':78C 'twist':79C 'unauthent':54B,111C 'use':57B 'version':171C 'vulner':165C 'wamp':73C 'websocket':5A,22B,39B,71C,112C 'without':31B,95C","nicknames":[],"mitigations":[],"who_affected":"Servers running Autobahn Python from `26.7.1` up to but not including `26.10.1` that enable the opt-in permessage-brotli feature through the compress extra. Deflate and bzip2 compression are not part of this issue. Deployments on other versions, or without permessage-brotli enabled, can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-26T21:18:15+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H","cvss_by":"security-advisories@github.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-116579","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-116579","severity":null,"published_at":"2026-10-26T21:18:15+00:00","modified_at":"2026-10-26T21:18:15+00:00","first_seen_at":"2026-10-26T21:20:31+00:00","fetched_at":"2026-10-26T21:20:31+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}