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Fencer Vulns
high 7.3

CVE-2026-100666 json

Netty 4.2.0 through 4.2.16 Response Desynchronization via HttpServerCodec

published 2026-09-26 44 d ago modified 2026-09-30 39 d ago also EUVD-2026-87760

cvss
7.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 22%
public exploits
0
none known

Summary

Netty's HttpServerCodec (io.netty:netty-codec-http) in versions 4.2.0.Final through 4.2.16.Final and in versions up to and including 4.1.136.Final pairs each outbound response with an inbound request by calling pollMethod() once per response, including for 1xx informational responses. If a client pipelines an HTTP/1.1 GET carrying an Expect: 100-continue header followed by a HEAD request, the 100 Continue response consumes the queued GET method, so the subsequent 200 OK for the GET is paired with HEAD and its body is dropped, while the following 200 OK for the HEAD request is written with a body. This desynchronizes HTTP parsing on the connection: the GET entity is never delivered and the HEAD response body is interpreted as the GET body, resulting in response splitting and unsafe connection reuse. Fixed in 4.2.17.Final and 4.1.137.Final.

Patch / fix

  • netty netty 4.1.137.Final, 4.2.17.Final

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-100666 updated cvss 7.3

io.netty/netty-codec-http: Netty: HTTP response desynchronization via HttpServerCodec

  • Red Hat Exploit Intelligence exploit-intelligence/agent-client-rhel9 Red Hat OpenShift Serverless openshift-serverless-1/kn-ekb-receiver-rhel9, openshift-serverless-1/kn-ekb-dispatcher-rhel9, openshift-serverless-1/kn-eventing-integrations-log-sink-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-s3-sink-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-sns-sink-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-sqs-sink-rhel9, +4 more Red Hat AMQ Clients netty-codec-http Red Hat build of Apache Camel for Spring Boot 4 netty-codec-http Red Hat build of Apicurio Registry 3 netty-codec-http Red Hat Build of Keycloak netty-codec-http, rhbk/keycloak-rhel9, keycloak/rhbk-rhel9-operator, rhbk/keycloak-rhel9-operator, keycloak/rhbk-openshift-rhel9
    +2 more products
    Red Hat Data Grid 8 netty-codec-http Red Hat Enterprise Linux AI (RHEL AI) 3 bazel6, bazel7, bazel8
    affected: workaround, no fix available
  • Red Hat JBoss Enterprise Application Platform 7 netty-codec-http, jboss-eap-7/eap74-els-openjdk8-openshift-rhel8, jboss-eap-7/eap74-els-openjdk11-openshift-rhel8, jboss-eap-7/eap74-els-openjdk17-openshift-rhel8
    affected: workaround, no fix planned “Will not fix”
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-modelmesh-rhel9, rhoai/odh-spark-operator-rhel9, rhoai/odh-trustyai-service-rhel9
    affected: workaround, no fix available
  • Red Hat Single Sign-On 7 netty-codec-http
    affected: workaround, no fix planned “Will not fix”
  • Red Hat Build of Debezium 3.6
    fixed: vendor fix RHSA-2026:83612
  • Red Hat JBoss Enterprise Application Platform 8.1
    fixed: vendor fix RHSA-2026:95887
  • Red Hat OpenShift Dev Spaces 3.31 devspaces/server-rhel9 1792775639, devspaces/openvsx-rhel9 1792494821, devspaces/jetbrains-ide-rhel9 1792476427, devspaces/pluginregistry-rhel9 1792495212, devspaces/multicluster-redirector-rhel9 1792491532
    fixed: vendor fix RHSA-2026:90321
  • Red Hat AMQ Broker 7 netty-codec-http Red Hat build of Apache Camel 4 for Quarkus 3 netty-codec-http Red Hat build of Quarkus netty-codec-http
    not affected: vulnerable code not present
show 5 more
  • Red Hat Fuse 7 netty-codec-http
    not affected: vulnerable code not in execute path
  • Red Hat JBoss Enterprise Application Platform Expansion Pack netty-codec-http
    not affected: component not present
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-th-torch-cpu-py312-rhel9, rhoai/odh-th-torch-cuda-py312-rhel9, rhoai/odh-th06-cpu-torch210-py312-rhel9, rhoai/odh-th06-cpu-torch291-py312-rhel9, rhoai/odh-th06-rocm64-torch291-py312-rhel9, rhoai/odh-th06-cuda130-torch210-py312-rhel9, +1 more
    not affected: vulnerable code not in execute path
  • Red Hat OpenShift Dev Spaces 3.31 devspaces/udi-rhel9 1792708612, devspaces/code-rhel9 1792599388, devspaces/traefik-rhel9 1792464177, devspaces/udi-base-rhel9 1792686842, devspaces/code-sshd-rhel9 1792598059, devspaces/dashboard-rhel9 1791945540, +5 more
    not affected: vulnerable code not present
  • Red Hat Satellite 6 candlepin, candlepin-selinux
    not affected: vulnerable code not in execute path

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
39 d ago

Exploit prediction

0.29% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/netty/netty/security/advisories/GHSA-2g6j-r8q9-5hr8 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N
CNA 3.1 7.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
CNA 4.0 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

  • netty netty

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.