Summary
AsyncHttpClient: Unbounded WebSocket permessage-deflate decompression enables a decompression-bomb denial of service when compression is enabled
Who is Impacted
Only 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://.
Affected versions
- 3.x: up to and including 3.0.13
- 2.x: from 2.2.0, when WebSocket compression was added, up to and including 2.16.1
Workarounds
Leave WebSocket compression disabled, which is the default.
Details
After 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.
This is a different path from the HTTP response decompression fixed under CVE-2026-85721, which never reached the WebSocket pipeline.
Attribution
AI-assisted tools were used to support discovery and analysis.
Impact
With 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.
A 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.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-107227 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.0.14); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Fixed 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.
The 2.x line is end of life and will not receive a fix. Upgrade to 3.0.14.
Frequently Asked Questions
- What is CVE-2026-107227? CVE-2026-107227 is a high-severity uncontrolled resource consumption vulnerability in org.asynchttpclient:async-http-client (maven), affecting versions >= 3.0.0, <= 3.0.13. It is fixed in 3.0.14. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-107227? CVE-2026-107227 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of org.asynchttpclient:async-http-client are affected by CVE-2026-107227? org.asynchttpclient:async-http-client (maven) versions >= 3.0.0, <= 3.0.13 is affected.
- Is there a fix for CVE-2026-107227? Yes. CVE-2026-107227 is fixed in 3.0.14. Upgrade to this version or later.
- Is CVE-2026-107227 exploitable, and should I be worried? Whether CVE-2026-107227 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-107227 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-107227? Upgrade
org.asynchttpclient:async-http-clientto 3.0.14 or later.