{"id":"CVE-2026-107227","aliases":["GHSA-x8v2-478q-2hvg"],"url":"https://o3.security/vulnerability/CVE-2026-107227","summary":"AsyncHttpClient: Unbounded WebSocket permessage-deflate decompression enables a decompression-bomb denial of service when compression is enabled","details":"### Impact\n\nWith WebSocket compression enabled, the client inflates `permessage-deflate` messages with no limit on the decompressed size. It installed Netty's shared `WebSocketClientCompressionHandler.INSTANCE`, whose inflater is unbounded, and `webSocketMaxFrameSize` and `webSocketMaxBufferSize` only bound the compressed bytes, because the frame aggregator sits in front of the inflater.\n\nA malicious or compromised WebSocket server, or anyone on the path of a `ws://` connection, can therefore send a message of about 2 MiB that inflates to about 2 GiB, the most a Netty buffer can hold. The client then copies the inflated message again to hand it to the listener. That exhausts the heap of a typically sized JVM. Netty catches the resulting `OutOfMemoryError` and closes that connection, but while the buffer is live any other allocation in the process can fail too, and a server that keeps sending such messages, on one connection or several, keeps the client at heap exhaustion.\n\n### Who is Impacted\n\nOnly applications that enable WebSocket compression with `setEnablewebSocketCompression(true)`, which is off by default, and connect to a WebSocket server that is untrusted, compromised, or reached over cleartext `ws://`.\n\n### Affected versions\n\n* 3.x: up to and including 3.0.13\n* 2.x: from 2.2.0, when WebSocket compression was added, up to and including 2.16.1\n\n### Patches\n\nFixed in 3.0.14. A new setting, `webSocketMaxDecompressedFrameSize` (`setWebSocketMaxDecompressedFrameSize`, or the `org.asynchttpclient.webSocketMaxDecompressedFrameSize` property), bounds how far a message may inflate, and a message that would go past it fails the connection. It defaults to 128000000 bytes, the same as `webSocketMaxBufferSize`, so a message is bounded alike whether or not it was compressed; a compressed message that inflates past that, which was accepted before, now fails the connection. With `aggregateWebSocketFrameFragments` turned off, the bound applies to each frame instead, and fragments are delivered one at a time. Set it lower if you enable compression and do not expect large messages. `0` disables the limit.\n\nThe 2.x line is end of life and will not receive a fix. Upgrade to 3.0.14.\n\n### Workarounds\n\nLeave WebSocket compression disabled, which is the default.\n\n### Details\n\nAfter the handshake the inbound pipeline is `ws-decoder`, `ws-aggregator`, `PerMessageDeflateDecoder`, `ahc-ws`: the aggregator, which enforces `webSocketMaxBufferSize`, sees each message before it is inflated. `WebSocketClientCompressionHandler.INSTANCE` is built with `maxAllocation = 0`, which Netty treats as unbounded, and Netty has deprecated it in favour of a constructor that takes a limit. RFC 6455 Section 10.4 asks an implementation to limit the size of a message after reassembly, and under RFC 7692 Section 6.2 the message delivered to the application is the decompressed payload.\n\nThis is a different path from the HTTP response decompression fixed under CVE-2026-85721, which never reached the WebSocket pipeline.\n\n### Attribution\n\nAI-assisted tools were used to support discovery and analysis.","published":"2026-10-07T20:51:04.823Z","modified":"2026-10-21T09:39:27.089509197Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Maven","name":"org.asynchttpclient:async-http-client","fixedVersion":"3.0.14"},{"ecosystem":"Maven","name":"org.asynchttpclient:async-http-client","fixedVersion":null}],"fix":{"url":"https://github.com/AsyncHttpClient/async-http-client/commit/b61637f30327f314b7693418f12ce141ac6b2b30","label":"AsyncHttpClient/async-http-client@b61637f"},"references":[{"type":"WEB","url":"https://github.com/AsyncHttpClient/async-http-client/releases/tag/async-http-client-project-3.0.14"},{"type":"ADVISORY","url":"https://github.com/AsyncHttpClient/async-http-client/security/advisories/GHSA-x8v2-478q-2hvg"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107227.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-107227"},{"type":"FIX","url":"https://github.com/AsyncHttpClient/async-http-client/commit/b61637f30327f314b7693418f12ce141ac6b2b30"},{"type":"PACKAGE","url":"https://github.com/AsyncHttpClient/async-http-client"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T09:39:27.089509197Z"}}