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Fencer Vulns
high 7.5

CVE-2026-9675 json

undici WebSocket client vulnerable to denial of service via cumulative fragment bypass

published 2026-06-17 4 mo ago modified 2026-06-25 4 mo ago also GHSA-38rv-x7px-6hhq , EUVD-2026-37752

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 37%
public exploits
0
none known

Summary

Impact: The undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service.

Affected applications are those using the undici WebSocket client (new WebSocket(...)) that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.

This is a regression specific to undici 8.1.0. The 6.25.0 line shipped the equivalent cumulative check from the start and is unaffected. The 7.x line never had the maxPayloadSize feature and is also unaffected.

Patches: Upgrade to undici >= 8.5.0.

Workarounds: No workaround is available. The fix must be applied through an upgrade.

Patch / fix

  • npm undici 8.5.0
  • undici undici 8.5.0
  • nodejs24 hummingbird 1 24.16.0-1.hum1
  • nodejs24-bin hummingbird 1 24.16.0-1.hum1
  • nodejs24-npm hummingbird 1 11.13.0-1.24.16.0.1.hum1
  • nodejs24-libs hummingbird 1 24.16.0-1.hum1
  • nodejs24-npm-bin hummingbird 1 24.16.0-1.hum1
  • nodejs24-full-i18n hummingbird 1 24.16.0-1.hum1
  • rust hummingbird 1 1.96.0-1.hum1
  • cargo hummingbird 1 1.96.0-1.hum1

red hat advisories RHSA-2026:25561RHSA-2026:22934RHSA-2026:22380RHSA-2026:7378

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-2026-9675 updated cvss 5.9

undici: undici WebSocket client vulnerable to denial of service via cumulative fragment bypass

  • Red Hat Self-service automation portal 2 ansible-automation-platform/bootc-automation-portal-rhel9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Hardened Images rust 1.96.0-1.hum1, cargo 1.96.0-1.hum1, clippy 1.96.0-1.hum1, rustfmt 1.96.0-1.hum1, rust-gdb 1.96.0-1.hum1, rust-src 1.96.0-1.hum1, +29 more
    fixed: vendor fix RHSA-2026:22934
  • Red Hat Cryostat 4 undici, grafana-infinity-datasource-npm, cryostat-openshift-console-plugin-npm Red Hat OpenShift Pipelines openshift-pipelines/pipelines-console-plugin-rhel8, openshift-pipelines/pipelines-console-plugin-rhel9, openshift-pipelines/pipelines-console-plugin-pf5-rhel9 Red Hat AMQ Broker 7 undici Red Hat Build of Podman Desktop rh-podman-desktop.git Red Hat Developer Hub 1 rhdh/rhdh-hub-rhel9 Red Hat Enterprise Linux 8 npm, nodejs, nodejs-libs, nodejs-nodemon, nodejs-full-i18n, nodejs-packaging, +1 more
    +9 more products
    Red Hat Enterprise Linux 9 npm, nodejs, nodejs-libs, nodejs-full-i18n Red Hat Enterprise Linux 10 nodejs22, nodejs24 Red Hat Hardened Images v8-13.6-devel 13.6.233.17-1.24.16.0.1.hum1, v8-14.1-devel 14.1.146.11-1.25.9.0.1.1.hum1, v8-14.6-devel 14.6.202.34-1.26.3.0.1.2.hum1 Red Hat OpenShift AI (RHOAI) rhoai/odh-dashboard-rhel9, rhoai/odh-mod-arch-maas-rhel9, rhoai/odh-mod-arch-automl-rhel9, rhoai/odh-mod-arch-gen-ai-rhel9, rhoai/odh-mod-arch-mlflow-rhel9, rhoai/odh-mod-arch-autorag-rhel9, +3 more Red Hat OpenShift Container Platform 4 openshift4/ose-console-rhel9, openshift4/ose-monitoring-plugin-rhel9, openshift4/ose-agent-installer-ui-rhel9 Red Hat OpenShift Container Platform 5 openshift5/ose-console-rhel9, openshift5/ose-agent-installer-ui-rhel9 Red Hat Openshift Data Foundation 4 odf4/odf-console-rhel9, odf4/ocs-client-console-rhel9, odf4/odf-multicluster-console-rhel9 Red Hat OpenShift Dev Spaces devspaces/code-rhel9, devspaces/openvsx-rhel9, devspaces/dashboard-rhel9, devspaces/pluginregistry-rhel9 Red Hat Self-service automation portal 2 ansible-automation-platform/automation-portal
    not affected: vulnerable code 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
yes
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.43% chance of exploitation in the next 30 days, higher than 37% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
npm undici
>=8.0.0, <8.5.0
8.5.0

Affected products

  • undici undici

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-770 Allocation of Resources Without Limits or Throttling

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.