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Fencer Intel
critical 9.1

CVE-2026-75595 json

Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext

published 2mo ago modified 16d ago also EUVD-2026-63095 , GHSA-c4c3-7fpv-j4q5

cvss
9.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 24%
public exploits
0
none known

Summary

Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Fina and 4.2.17.Final, io.netty.handler.ssl.SslClientHelloHandler#decode checks the wrong offset before reading the four-byte TLS handshake header, so a ClientHello whose handshake header spans records can cause an IndexOutOfBoundsException and invoke select(ctx, null). This selects the default SslContext instead of the SNI-specific context. In deployments where per-SNI clientAuth=REQUIRE is the sole mutual TLS gate, the default SslContext uses clientAuth=NONE or clientAuth=OPTIONAL, and no application-layer certificate verification exists, an unauthenticated remote attacker can bypass the protected route's mutual TLS requirement. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

Patch / fix

  • maven io.netty:netty-handler 4.1.137.Final, 4.2.17.Final
  • io.netty netty-handler 4.1.137.Final, 4.2.17.Final
  • netty netty-handler 4.1.137.Final, 4.2.17.Final
  • netty-tcnative SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 2.0.84-150200.3.51.1
  • netty SLE Module for Package Hub 15 SP7 4.1.138-150200.4.56.1

suse advisories SUSE-SU-2026:4391-1

  • netty openSUSE Tumbleweed 4.1.138-1.1

opensuse advisories openSUSE-SU-2026:11882-1

Is CVE-2026-75595 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

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-2026-75595 updated cvss 7.4

io.netty/netty-handler: Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext

  • Red Hat AMQ Clients netty-handler Red Hat build of Apicurio Registry 3 netty-handler Red Hat Ceph Storage 9 libarrow, parquet-libs Red Hat Data Grid 8 netty-handler
    affected: workaround, no fix available
  • Red Hat Fuse 7 netty-handler
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat JBoss Enterprise Application Platform 7 netty-handler
    affected: workaround, no fix planned “Will not fix”
  • Red Hat OpenShift Dev Spaces devspaces/server-rhel9, devspaces/openvsx-rhel9, devspaces/jetbrains-ide-rhel9, devspaces/pluginregistry-rhel9, devspaces/multicluster-redirector-rhel9
    affected: workaround, no fix available
  • Red Hat Single Sign-On 7 netty-handler
    affected: workaround, no fix planned “Out of support scope”
  • 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 Enterprise Linux AI (RHEL AI) 3 bazel6, bazel7, bazel8 Red Hat Offline Knowledge Portal offline-knowledge-portal/rhokp-rhel9, redhat-user-workloads/rhocc-mimir-tenant/mimir/rhokp-core-encrypted Red Hat OpenShift AI (RHOAI) rhoai/odh-modelmesh-rhel9, rhoai/odh-spark-operator-rhel9, rhoai/odh-trustyai-service-rhel9, rhoai/odh-th-torch-cpu-py312-rhel9, rhoai/odh-th-torch-cuda-py312-rhel9, rhoai/odh-th06-cpu-torch210-py312-rhel9, +4 more Red Hat OpenStack Platform 13 (Queens) opendaylight
    +1 more products
    Red Hat Satellite 6 candlepin, candlepin-selinux
    under investigation
  • Red Hat build of Apache Camel 4.18.4 for Spring Boot 3.5.16
    fixed: vendor fix RHSA-2026:71675
  • Red Hat Build of Debezium 3.6
    fixed: vendor fix RHSA-2026:83612
show 7 more
  • Red Hat build of Keycloak 26.4 rhbk/keycloak-rhel9 26.4-29, rhbk/keycloak-rhel9-operator 26.4-30, rhbk/keycloak-operator-bundle 26.4.17-2
    fixed: vendor fix RHSA-2026:95760
  • Red Hat build of Keycloak 26.4.17
    fixed: vendor fix RHSA-2026:95759
  • Red Hat build of Keycloak 26.6 rhbk/keycloak-rhel9 26.6-24, rhbk/keycloak-rhel9-operator 26.6-24, rhbk/keycloak-operator-bundle 26.6.8-2
    fixed: vendor fix RHSA-2026:95762
  • Red Hat build of Keycloak 26.6.8
    fixed: vendor fix RHSA-2026:95761
  • Red Hat JBoss Enterprise Application Platform 8.1
    fixed: vendor fix RHSA-2026:95887
  • Red Hat AMQ Broker 7 netty-handler Red Hat build of Apache Camel 4 for Quarkus 3 netty-handler Red Hat build of Quarkus netty-handler
    not affected: vulnerable code not present
  • Red Hat JBoss Enterprise Application Platform Expansion Pack netty-handler
    not affected: component not present

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
none
Automatable
no
Technical impact
total
Assessed
2mo ago

Exploit prediction

0.32% chance of exploitation in the next 30 days, higher than 24% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 4.0 9.1 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
CNA 4.0 9.1 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/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
NVD 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected packages

ecosystem package affected fixed in
maven io.netty:netty-handler
>=4.2.0.Final, <4.2.17.Final
<4.1.137.Final
4.2.17.Final
4.1.137.Final

Affected products

  • netty netty

Classification

Weakness
  • CWE-754 Improper Check for Unusual or Exceptional Conditions
  • CWE-475 Undefined Behavior for Input to API

References

Sources

Fencer Intel 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.