Netty before 4.1.138.Final Denial of Service via WebSocketServerExtensionHandler (CVE-2026-100658) | HOL Guard CVE

Medium · CVSS 6.9CVE-2026-100658

Netty before 4.1.138.Final Denial of Service via WebSocketServerExtensionHandler

Answer in brief

CVE-2026-100658 records a Medium severity (CVSS 6.9) vulnerability in Netty before 4.1.138.Final Denial of Service via WebSocketServerExtensionHandler. The current sources do not mark it as known exploited. The current feed maps netty/netty (generic), netty/netty (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 26, 2026Updated Sep 26, 2026Source checked Sep 26, 2026First seen by HOL Sep 26, 2026Material review Sep 26, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 6.9
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 6.9. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps netty/netty (generic), netty/netty (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
netty/nettygeneric	>=4.1.88.Final <4.1.138.Final	4.1.138.Final
netty/nettygeneric	>=4.2.0.Final <4.2.18.Final	4.2.18.Final

Recommended response

Check inventory. Check lockfiles and deployed manifests for netty/netty, netty/netty.
Review the reported fix. Update netty/netty to 4.1.138.Final; netty/netty to 4.2.18.Final if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 26, 2026

Sources and claim methodology

Upstream source description

Netty (io.netty:netty-codec-http) contains an unbounded per-connection queue in WebSocketServerExtensionHandler. The handler offers an entry to its per-channel validExtensions queue for every inbound HttpRequest, but polls an entry only when the application writes an HttpResponse, and the queue size is never bounded. A remote, unauthenticated peer can use HTTP/1.1 pipelining to send requests faster than the application produces responses — including plain non-upgrade HTTP requests to any path — causing the queue to grow without limit until the JVM exhausts heap memory and terminates with OutOfMemoryError. Because the affected handler is the base class of WebSocketServerCompressionHandler, any server that enables permessage-deflate is exposed on its plain HTTP port before any WebSocket upgrade completes and before any application-level authentication. Affected versions are 4.1.88.Final through 4.1.137.Final and 4.2.0.Final through 4.2.17.Final; the issue is fixed in 4.1.138.Final and 4.2.18.Final.

Quoted source text, attributed separately from HOL analysis.