CVE-2026-107227 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in org.asynchttpclient:async-http-client. A fix is available for org.asynchttpclient:async-http-client — see the affected versions and patch details below.
AsyncHttpClient: Unbounded WebSocket permessage-deflate decompression enables a decompression-bomb denial of service when compression is enabled
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-107227.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-107227 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,415 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
org.asynchttpclient:async-http-client☕org.asynchttpclient:async-http-clientReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
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.
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
Patches
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.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.asynchttpclient:async-http-client | ≥ 3.0.0&&< 3.0.14 | 3.0.14org.asynchttpclient:async-http-client:3.0.14 |
| ☕Maven | org.asynchttpclient:async-http-client | ≥ 2.2.0 | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.asynchttpclient:async-http-client, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.asynchttpclient:async-http-client to 3.0.14 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-107227 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is CVE-2026-107227 in your dependencies?
Find it across Maven, including transitive dependencies.