CVE-2025-66418 json
urllib3 allows an unbounded number of links in the decompression chain
published 11mo ago modified last mo. also EUVD-2025-201421 , GHSA-gm62-xv2j-4w53 , PYSEC-2026-1998
- cvss
- 7.5
- version 3.1, NVD
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.7%
- EPSS 0.7% chance of exploitation in 30 days, percentile 54%
- public exploits
- 0
- none known
Summary
urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0.
Patch / fix
- pypi urllib3 2.6.0
- python urllib3 2.6.0
- python-urllib3 Debian 12 1.26.12-1+deb12u2
- python-urllib3 Debian 13 2.3.0-3+deb13u1
- python-urllib3 Debian 14 2.5.0-1.1
debian advisories DEBIAN-CVE-2025-66418
- python-urllib3 Ubuntu 22.04 LTS 1.26.5-1~exp1ubuntu0.4
- python-urllib3 Ubuntu 24.04 LTS 2.0.7-1ubuntu0.3
- python-urllib3 Ubuntu 25.10 2.3.0-3ubuntu0.1
- python-urllib3 Ubuntu 26.04 LTS 2.5.0-1ubuntu1
- python-pip Ubuntu Pro 22.04 LTS 22.0.2+dfsg-1ubuntu0.7+esm1
- python-pip Ubuntu Pro 24.04 LTS 24.0+dfsg-1ubuntu1.3+esm1
- python-urllib3 Ubuntu Pro 20.04 LTS 1.25.8-2ubuntu0.4+esm2
ubuntu advisories UBUNTU-CVE-2025-66418
Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0
- python-urllib3 openstack 17.1 1.26.5-3.el8ost.3
- python3-urllib3 openstack 17.1 1.26.5-3.el8ost.3
- python-urllib3 satellite capsule 6.16, satellite 6.16 2.6.3-0.1.el8pc
- python-urllib3 satellite capsule 6.17, satellite capsule 6.16, satellite 6.17 +1 more 2.6.3-0.1.el9pc
- python3.11-urllib3 satellite capsule 6.16, satellite 6.16 2.6.3-0.1.el8pc
- python3.11-urllib3 satellite capsule 6.17, satellite capsule 6.16, satellite 6.17 +1 more 2.6.3-0.1.el9pc
- python-urllib3 rhui 4 2.6.3-1.el8ui
- python3.11-urllib3 rhui 4 2.6.3-1.el8ui
red hat advisories RHSA-2026:28043RHSA-2026:2765RHSA-2026:2764RHSA-2026:2728RHSA-2026:2723RHSA-2026:2717
- python-urllib3 SLE Module for Python 3 15 SP7, SLE Module for Public Cloud 15 SP4, SLE High Performance Computing 15 SP5-ESPOS +10 more 2.0.7-150400.7.27.1
- python-urllib3 SLES LTSS Extended Security 12 SP5, SLE Module for Public Cloud 12 1.25.10-3.48.4
- python-urllib3_1 SLES for SAP applications 16.0, SLES 16.0 1.26.20-160000.3.1
- python-urllib3_1 SLE Module for Python 3 15 SP7, openSUSE Leap 15.6 1.26.18-150600.3.6.1
- python-urllib3 Linux Micro 6.1 2.1.0-slfo.1.1_4.1
- python-urllib3 Linux Micro 6.0 2.1.0-5.1
- python-urllib3 SLE Module for Basesystem 15 SP7, SLE Micro 5.5, SLE Micro 5.4 +2 more 1.25.10-150300.4.21.1
- python-urllib3 SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 2.5.0-160000.4.1
suse advisories SUSE-SU-2026:0367-2SUSE-SU-2026:1412-1SUSE-SU-2026:20591-1SUSE-SU-2026:0635-1SUSE-SU-2026:20485-1SUSE-SU-2026:20443-1
- oci-cli openSUSE Tumbleweed 3.76.2-1.1
- python-oci-sdk openSUSE Tumbleweed 2.168.3-1.1
- python-urllib3_1 openSUSE Leap 16.0 1.26.20-160000.3.1
- python-urllib3 openSUSE Leap 16.0 2.5.0-160000.4.1
- python-urllib3_1 openSUSE Tumbleweed 1.26.20-5.1
- python-urllib3 openSUSE Tumbleweed 2.6.2-1.1
opensuse advisories openSUSE-SU-2026:10539-1openSUSE-SU-2026:10431-1openSUSE-SU-2026:20271-1openSUSE-SU-2026:20127-1openSUSE-SU-2026:10096-1openSUSE-SU-2026:10026-1
- python3-urllib3 AlmaLinux 10 1.26.19-2.el10_1.1
- python3-urllib3 AlmaLinux 9 1.26.5-6.el9_7.1
- python3.12-urllib3 AlmaLinux 9 1.26.19-1.el9_7.1
- python3.11-urllib3 AlmaLinux 9 1.26.12-5.el9_7.1
- python3.11-urllib3 AlmaLinux 8 1.26.12-6.el8_10
- python3.12-urllib3 AlmaLinux 8 1.26.19-2.el8_10
- fence-virt AlmaLinux 9 4.10.0-98.el9_7.4
- fence-virtd AlmaLinux 9 4.10.0-98.el9_7.4
almalinux advisories ALSA-2026:1086ALSA-2026:1087ALSA-2026:1088ALSA-2026:1089ALSA-2026:1224ALSA-2026:1226
- fence-agents Rocky Linux 8 4.2.1-129.el8_10.20
- python-urllib3 Rocky Linux 10 1.26.19-2.el10_1.1
- python-urllib3 Rocky Linux 9 1.26.5-6.el9_7.1
- python3.12-urllib3 Rocky Linux 9 1.26.19-1.el9_7.1
- python3.11-urllib3 Rocky Linux 9 1.26.12-5.el9_7.1
- fence-agents Rocky Linux 9 4.10.0-98.el9_7.4
- resource-agents Rocky Linux 8 4.9.0-54.el8_10.27
- python3.11-urllib3 Rocky Linux 8 1.26.12-6.el8_10
rocky linux advisories RLSA-2026:1240RLSA-2026:1086RLSA-2026:1087RLSA-2026:1088RLSA-2026:1089RLSA-2026:1239
- py3-urllib3 Alpine 3.23 2.6.3-r0
alpine advisories ALPINE-CVE-2025-66418
Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0
- python-urllib3 Azure Linux 3.0 2.0.7-3
- python-urllib3 CBL-Mariner 2.0 1.26.19-3
azure linux advisories AZL-71834AZL-71846
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
Is CVE-2025-66418 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 FencerVendor advisories
What the vendors themselves say about their products: affected, fixed or not affected, and what to do.
red hat product security vex CVE-2025-66418 updated cvss 7.5
urllib3: urllib3: Unbounded decompression chain leads to resource exhaustion
-
Red Hat Assisted Installer for Red Hat OpenShift Container Platform 2 rhai/assisted-installer-agent-rhel9, rhai/assisted-installer-controller-rhel9affected: workaround, no fix planned “Will not fix”
-
Red Hat cert-manager Operator for Red Hat OpenShift cert-manager/cert-manager-istio-csr-rhel9 Red Hat Confidential Compute Attestation build-of-trustee/trustee-rhel9, openshift-sandboxed-containers/osc-podvm-payload-rhel9, confidential-compute-attestation-tech-preview/trustee-rhel9affected: workaround, no fix available
-
Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/vector-rhel9, openshift-logging/kibana6-rhel8, openshift-logging/elasticsearch6-rhel9, openshift-logging/logging-curator5-rhel9, openshift-logging/elasticsearch-proxy-rhel9affected: workaround, no fix planned “Will not fix”
-
Red Hat Migration Toolkit for Containers rhmtc/openshift-migration-rhel8-operator, rhmtc/openshift-migration-hook-runner-rhel8 Red Hat Migration Toolkit for Virtualization mtv-candidate/mtv-rhel9-operator, mtv-candidate/mtv-virt-v2v-rhel9, mtv-candidate/mtv-must-gather-rhel8, mtv-candidate/mtv-cli-download-rhel9, mtv-candidate/mtv-console-plugin-rhel9, migration-toolkit-virtualization/mtv-virt-v2v-rhel9affected: workaround, no fix available, no fix planned “Will not fix”
-
Red Hat Multiarch Tuning Operator multiarch-tuning/multiarch-tuning-rhel9-operatoraffected: workaround, no fix available
-
Red Hat Multicluster Engine for Kubernetes multicluster-engine/assisted-service-8-rhel8, multicluster-engine/assisted-service-9-rhel9, multicluster-engine/assisted-installer-agent-rhel9, multicluster-engine/assisted-installer-controller-rhel9affected: workaround, no fix planned “Will not fix”
-
Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-service-api-rhel9, openshift-lightspeed-tech-preview/lightspeed-rag-tool-rhel9, openshift-lightspeed/lightspeed-to-dataverse-exporter-rhel9affected: workaround, no fix available
-
Red Hat OpenShift Pipelines openshift-pipelines/pipelines-events-rhel8, openshift-pipelines/pipelines-hub-ui-rhel8, openshift-pipelines/pipelines-hub-ui-rhel9, openshift-pipelines/pipelines-cli-tkn-rhel8, openshift-pipelines/pipelines-hub-api-rhel8, openshift-pipelines/pipelines-webhook-rhel8, +27 moreaffected: workaround, no fix available, no fix planned “Will not fix”
show 22 moreshow fewer
-
Red Hat OpenShift Serverless openshift-serverless-1/kn-eventing-integrations-transform-jsonata-rhel9affected: workaround, no fix available
-
Red Hat AI Inference Server rhaiis/vllm-tpu-rhel9, rhaiis/vllm-spyre-rhel9, rhai/base-image-cpu-rhel9, rhai/base-image-cuda-rhel9, rhai/base-image-rocm-rhel9, rhaiis-preview/vllm-cuda-rhel9affected: workaround, no fix available, no fix planned “Out of support scope”
-
Red Hat Ansible Automation Platform 2 automation-controller, ansible-automation-platform-26/gateway-rhel9, ansible-automation-platform-25/receptor-rhel8, ansible-automation-platform-24/ee-minimal-rhel8, ansible-automation-platform-24/ee-minimal-rhel9, ansible-automation-platform-25/de-minimal-rhel8, +25 moreaffected: workaround, no fix available, no fix planned “Will not fix”
-
Red Hat build of Quarkus Native builder quarkus-mandrel#109bb34d7147bcc055f0f7f53427ebb8cb02f86d, quarkus-mandrel#602dee7389eeb13bfb88aa7242da02d0161ee946 Red Hat Ceph Storage 6 urllib3 Red Hat Ceph Storage 7 urllib3 Red Hat Ceph Storage 9 urllib3 Red Hat Certification Program for Red Hat Enterprise Linux 9 rhcertification/redhat-certification-baremetal, rhcertification/redhat-certification-system-aiaffected: workaround, no fix available
-
Red Hat Connectivity Link 1 rhcl-1/limitador-rhel9, rhcl-1/wasm-shim-rhel9, rhcl-1/rhcl-console-plugin-rhel9affected: workaround, no fix available, no fix planned “Will not fix”
-
Red Hat Developer Hub 1 rhdh/rhdh-hub-rhel9affected: workaround, no fix available “Fix deferred”
-
Red Hat Edge Manager preview rhem/flightctl-db-setup-rhel9, rhem/flightctl-cli-artifacts-rhel9 Red Hat Enterprise Linux 8 ubi8, ubi8/ubi, rhel8/pcp, ubi8-init, rhel8/cups, ubi8/php-74, +63 moreaffected: workaround, no fix available
-
Red Hat Enterprise Linux 9 ubi9, ubi9/ubi, rhel9/pcp, ubi9-init, rhel9/cups, rhel9/rtla, +89 more Red Hat Enterprise Linux 10 ubi10, ubi10/ubi, rhel10/pcp, ubi10-init, rhel10/cups, rhel10/rtla, +53 moreaffected: workaround, no fix available, no fix planned “Will not fix”
-
Red Hat Enterprise Linux AI (RHEL AI) rhelai1/bootc-amd-rhel9, rhelai1/bootc-intel-rhel9, rhelai1/bootc-nvidia-rhel9, rhelai1/bootc-azure-amd-rhel9, rhelai1/instructlab-amd-rhel9, rhelai1/bootc-aws-nvidia-rhel9, +4 more Red Hat Enterprise Linux AI (RHEL AI) 3 rhelai3/bootc-cuda-rhel9, rhelai3/bootc-aws-cuda-rhel9, rhelai3/bootc-gcp-cuda-rhel9, rhelai3/disk-image-cuda-rhel9, rhelai3/bootc-azure-cuda-rhel9affected: workaround, no fix planned “Will not fix”
-
Red Hat OpenShift Container Platform 4 openshift4/rdma-cni-rhel9, openshift4/ose-ironic-rhel9, openshift4/network-tools-rhel9, openshift4/ose-ironic-agent-rhel9, openshift4/egress-router-cni-rhel9, openshift4/ose-egress-router-rhel9, +17 more Red Hat Openshift Data Foundation 4 odf4/mcg-core-rhel9, odf4/odf-must-gather-rhel9, odf4/ocs-client-console-rhel9, odf4/rook-ceph-rhel9-operator, odf4/ocs-metrics-exporter-rhel9affected: workaround, no fix available
-
Red Hat OpenShift Dev Spaces devspaces-tech-preview/jetbrains-ide-rhel9affected: workaround, no fix planned “Will not fix”
-
Red Hat Satellite 6 python-urllib3, python3-urllib3, satellite/iop-vmaas-rhel9, satellite/iop-yuptoo-rhel9, satellite/iop-gateway-rhel9, satellite/iop-host-inventory-rhel9, +1 moreaffected: workaround, no fix available
-
Red Hat Builds for Red Hat OpenShift 1.6.0 openshift-builds 1.6.2-1767088114, openshift-builds 1.6.2-1767088118fixed: vendor fix RHSA-2026:0050
-
Red Hat Cert Manager support for Red Hat OpenShift release 1.18 cert-manager 1768985286, cert-manager 1769093352, cert-manager 1769093421, cert-manager 1769419247, cert-manager 1769419291, cert-manager 1769419550fixed: vendor fix RHSA-2026:1176
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Red Hat mirror registry for Red Hat OpenShift 2.0 openshift/mirror-registry-rhel8 1782177012fixed: vendor fix RHSA-2026:28441
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Red Hat Multicluster Global Hub 1.4.9 multicluster-globalhub 1770126537fixed: vendor fix RHSA-2026:2500
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Red Hat Multicluster Global Hub 1.5.8 multicluster-globalhub 1770109405fixed: vendor fix RHSA-2026:2256
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Red Hat Network Observability (NETOBSERV) 1.11.0 network-observability 1771226060fixed: vendor fix RHSA-2026:2900
-
Red Hat OpenShift API for Data Protection 1.3 oadp 1770420495, oadp 1770420562, oadp 1770420563, oadp 1770420565, oadp 1770420728, oadp 1770420975, +4 morefixed: vendor fix RHSA-2026:3444
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Red Hat Advanced Cluster Security 4.8 advanced-cluster-security 1771402244, advanced-cluster-security 1772474383, advanced-cluster-security 1773235880fixed: vendor fix RHSA-2026:4466
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Red Hat Advanced Cluster Security 4.9 advanced-cluster-security 1771401314, advanced-cluster-security 1772473062, advanced-cluster-security 1773235860fixed: vendor fix RHSA-2026:4467
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Red Hat AI Inference Server 3.2 rhaiis 1772160593, rhaiis 1772160625, rhaiis/vllm-cuda-rhel9 1787860580, rhaiis/vllm-rocm-rhel9 1787884873, rhaiis/model-opt-cuda-rhel9 1787772157fixed: vendor fix RHSA-2026:61628
86 more fixed, 72 more not affected in the full advisory
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
- 11mo ago
Exploit prediction
0.73% chance of exploitation in the next 30 days, higher than 54% of all scored CVEs (FIRST EPSS, 2026-11-09).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 8.9 | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H |
| CNA | 4.0 | 8.9 | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/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 | 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 |
|---|---|---|---|
| pypi | urllib3 | >=1.24, <2.6.0 |
2.6.0 |
Affected products
- urllib3 urllib3
Classification
- Weakness
-
- CWE-770 Allocation of Resources Without Limits or Throttling
References
-
github.com
/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8
web, patch
-
github.com
/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53
web, vendor-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2025-66418
advisory
-
github.com
/urllib3/urllib3
package
-
pypi.org
/project/urllib3
package
-
github.com
/advisories/GHSA-gm62-xv2j-4w53
advisory
Sources
- CVE List CVE-2025-66418
- GitHub Advisory GHSA-gm62-xv2j-4w53
- NVD CVE-2025-66418
- OSV PYSEC-2026-1998
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.