Netty 4.2.0 through 4.2.18 HTTP/3 Request Routing Bypass (CVE-2026-100659) | HOL Guard CVE

Medium · CVSS 6.9CVE-2026-100659

Netty 4.2.0 through 4.2.18 HTTP/3 Request Routing Bypass

Answer in brief

CVE-2026-100659 records a Medium severity (CVSS 6.9) vulnerability in Netty 4.2.0 through 4.2.18 HTTP/3 Request Routing Bypass. The current sources do not mark it as known exploited. The current feed maps 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: 1 mapped package or product
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). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
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.
Review the reported fix. Update 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's HTTP/3 codec (io.netty:netty-codec-http3) in versions 4.2.0.Final through 4.2.17.Final does not enforce the RFC 9114 requirement that the :authority pseudo-header field and a literal host header field, when both present, carry the same value. A remote unauthenticated peer can send a single HEADERS frame containing both fields with differing, attacker-controlled values; the request is accepted and delivered to the application with two conflicting authorities, allowing routing, virtual-host, and access-control decisions to be bypassed when different components in the request path consult different fields. This issue is fixed in 4.2.18.Final.

Quoted source text, attributed separately from HOL analysis.