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Fencer Vulns
low 3.7

CVE-2026-11525 json

undici vulnerable to Set-Cookie SameSite attribute downgrade via permissive substring matching

published 2026-06-17 4 mo ago modified 2026-09-10 1 mo ago also GHSA-g8m3-5g58-fq7m , EUVD-2026-37758

cvss
3.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 14%
public exploits
0
none known

Summary

Impact: When undici parses a Set-Cookie header, it accepts any SameSite attribute value that contains Strict, Lax, or None as a substring, rather than the case-insensitive exact match specified by RFC 6265. Non-spec values are silently mapped to one of the three standard tokens. For example, SameSite=NoneOfYourBusiness is parsed as None (the most permissive setting), and SameSite=StrictLax is parsed as Lax (a downgrade from Strict).

Affected applications are those that consume Set-Cookie headers from server responses (for example via undici's fetch or proxy code paths) and then forward or rely on the parsed sameSite attribute. A malicious or non-compliant server can coerce the consumer's view of a cookie's SameSite policy to a weaker value, silently degrading the SameSite enforcement the cookie is supposed to provide.

This was introduced in undici 5.15.0 when the cookies feature was added.

Patches: Upgrade to undici v6.26.0, v7.28.0 or v8.5.0.

Workarounds: After parsing a Set-Cookie header, validate that the resulting sameSite attribute is one of 'Strict', 'Lax', or 'None' (exact, case-insensitive) before forwarding or relying on it.

Patch / fix

  • npm undici 6.27.0, 7.28.0, 8.5.0
  • undici undici 6.26.0, 7.28.0, 8.5.0
  • node-undici Debian 14 8.5.0+dfsg+~cs3.2.0-1

debian advisories DEBIAN-CVE-2026-11525

  • nodejs26 hummingbird 1 26.5.0-1.5.hum1
  • nodejs26-bin hummingbird 1 26.5.0-1.5.hum1
  • nodejs26-npm hummingbird 1 11.17.0-1.26.5.0.1.5.hum1
  • nodejs26-libs hummingbird 1 26.5.0-1.5.hum1
  • nodejs26-npm-bin hummingbird 1 26.5.0-1.5.hum1
  • nodejs26-full-i18n hummingbird 1 26.5.0-1.5.hum1
  • npm RHEL 8 1:10.9.8-1.22.23.1.1.module+el8.10.0+24500+8eb51621
  • nodejs RHEL 8 1:22.23.1-1.module+el8.10.0+24500+8eb51621

red hat advisories RHSA-2026:45783RHSA-2026:41947RHSA-2026:39868RHSA-2026:38236RHSA-2026:35891RHSA-2026:35892

  • nodejs16 SLES for SAP 15 SP4, SLES 15 SP4-LTSS, SLE High Performance Computing 15 SP4-LTSS +1 more 16.20.2-150400.3.42.1
  • nodejs18 SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +5 more 18.20.8-150400.9.39.1
  • nodejs20 SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 20.20.2-150500.11.30.1
  • nodejs24 SLES for SAP applications 16.0, SLES 16.0 24.18.0-160000.1.1
  • nodejs22 SLE Module for Web and Scripting 15 SP7 22.23.0-150700.3.12.1
  • nodejs24 SLE Module for Web and Scripting 15 SP7 24.17.0-150700.15.11.1
  • nodejs22 SLES for SAP applications 16.0, SLES 16.0 22.23.0-160000.1.1
  • nodejs18 SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 18.20.8-8.44.1

suse advisories SUSE-SU-2026:4355-1SUSE-SU-2026:4261-1SUSE-SU-2026:4248-1SUSE-SU-2026:3930-1SUSE-SU-2026:3929-1SUSE-SU-2026:22565-1

  • nodejs24 openSUSE Leap 16.0 24.18.0-160000.1.1
  • nodejs22 openSUSE Leap 16.0 22.23.0-160000.1.1
  • nodejs24 openSUSE Tumbleweed 24.17.0-1.1

opensuse advisories openSUSE-SU-2026:21236-1openSUSE-SU-2026:21058-1openSUSE-SU-2026:11121-1

  • npm AlmaLinux 8 1:10.9.8-1.22.23.1.1.module_el8.10.0+4231+1bf2f855
  • nodejs AlmaLinux 8 1:22.23.1-1.module_el8.10.0+4231+1bf2f855
  • nodejs-libs AlmaLinux 8 1:22.23.1-1.module_el8.10.0+4231+1bf2f855
  • nodejs-nodemon AlmaLinux 8 3.0.1-1.module_el8.10.0+3956+47c9ee9f
  • nodejs-full-i18n AlmaLinux 8 1:22.23.1-1.module_el8.10.0+4231+1bf2f855
  • nodejs-packaging AlmaLinux 8 2021.06-6.module_el8.10.0+4158+e796f37f
  • nodejs-packaging-bundler AlmaLinux 8 2021.06-6.module_el8.10.0+4158+e796f37f
  • npm AlmaLinux 8 1:11.16.0-1.24.18.0.1.module_el8.10.0+4228+2938bc94

almalinux advisories ALSA-2026:41947ALSA-2026:39868ALSA-2026:35841ALSA-2026:35842ALSA-2026:35891ALSA-2026:35892

  • nodejs-nodemon Rocky Linux 8 3.0.1-1.module+el8.9.0+1760+903d54b9
  • nodejs-nodemon Rocky Linux 8 3.0.1-1.module+el8.10.0+1667+4a788d89
  • nodejs-nodemon Rocky Linux 8 3.0.1-1.module+el8.10.0+1824+532140ee
  • nodejs-nodemon Rocky Linux 8 3.0.1-1.module+el8.10.0+1823+b5789597
  • nodejs-nodemon Rocky Linux 8 3.0.1-1.module+el8.10.0+1924+614dc87f
  • nodejs-nodemon Rocky Linux 8 3.0.1-1.module+el8.10.0+1666+930e28e8
  • nodejs-nodemon Rocky Linux 8 3.0.1-1.module+el8.10.0+1988+437f3d23
  • nodejs-nodemon Rocky Linux 8 3.0.1-1.module+el8.10.0+1989+e60144d9

rocky linux advisories RLSA-2026:41947RLSA-2026:39868RLSA-2026:35841RLSA-2026:35842RLSA-2026:35891RLSA-2026:35892

  • nodejs Azure Linux 3.0 24.18.1-1

azure linux advisories AZL-91194

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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-2026-11525 updated cvss 3.7

undici: undici: Weakening of cookie SameSite policy due to incorrect parsing of Set-Cookie header

  • 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
    +6 more products
    Red Hat Hardened Images nodejs25 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 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, ansible-automation-platform/bootc-automation-portal-rhel9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux AppStream (v. 8) nodejs 22.23.1-1.module+el8.10.0+24500+8eb51621, nodejs 24.18.0-1.module+el8.10.0+24481+7a71fac8, nodejs-libs 22.23.1-1.module+el8.10.0+24500+8eb51621, nodejs-libs 24.18.0-1.module+el8.10.0+24481+7a71fac8, nodejs-nodemon 3.0.1-1.module+el8.10.0+24500+8eb51621, nodejs-nodemon 3.0.3-1.module+el8.10.0+24190+49a46c75, +8 more
    fixed: vendor fix RHSA-2026:41947
  • Red Hat Enterprise Linux AppStream (v. 9) nodejs 22.23.1-1.module+el9.8.0+24457+996af7aa, nodejs 24.18.0-1.module+el9.8.0+24456+b244c3b4, nodejs-libs 22.23.1-1.module+el9.8.0+24457+996af7aa, nodejs-libs 24.18.0-1.module+el9.8.0+24456+b244c3b4, nodejs-nodemon 3.0.1-1.module+el9.8.0+24156+bb41d456, nodejs-nodemon 3.0.3-3.module+el9.8.0+24355+35d95b59, +8 more
    fixed: vendor fix RHSA-2026:35892
  • Red Hat Enterprise Linux AppStream (v. 10) nodejs 22.23.1-2.el10_2, nodejs22 22.23.1-2.el10_2, nodejs24 24.18.0-1.el10_2, nodejs-libs 22.23.1-2.el10_2, nodejs24-libs 24.18.0-1.el10_2, nodejs-full-i18n 22.23.1-2.el10_2, +3 more
    fixed: vendor fix RHSA-2026:35842
  • Red Hat Hardened Images nodejs26 26.5.0-1.5.hum1, nodejs24 24.18.0-0.3.hum1, nodejs26-bin 26.5.0-1.5.hum1, nodejs24-bin 24.18.0-0.3.hum1, nodejs26-libs 26.5.0-1.5.hum1, nodejs24-libs 24.18.0-0.3.hum1, +6 more
    fixed: vendor fix RHSA-2026:38236
  • Red Hat Openshift Data Foundation 4.18 odf4/cephcsi-rhel9 1786705347, odf4/odf-cli-rhel9 1786705938, odf4/mcg-core-rhel9 1786705558, odf4/odf-console-rhel9 1786706577, odf4/mcg-rhel9-operator 1786705646, odf4/ocs-rhel9-operator 1786705802, +13 more
    fixed: vendor fix RHSA-2026:56431
  • Red Hat Hardened Images rust Red Hat Openshift Data Foundation 4.18 odf4/mcg-operator-bundle 1786708633, odf4/ocs-operator-bundle 1786708778, odf4/odf-operator-bundle 1786709119, odf4/cephcsi-operator-bundle 1786708508, odf4/odr-hub-operator-bundle 1786709184, odf4/rook-ceph-operator-bundle 1786709254, +7 more
    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
no
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.24% chance of exploitation in the next 30 days, higher than 14% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
GitHub 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
npm undici
<6.27.0
>=7.0.0, <7.28.0
>=8.0.0, <8.5.0
6.27.0
7.28.0
8.5.0

Affected products

  • undici undici

Classification

Weakness
  • CWE-183 Permissive List of Allowed Inputs

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.