Vulnerability · Published Dec 5, 2025 · Assigned by GitHub_M
CVE-2025-66418urllib3 allows an unbounded number of links in the decompression chain
High 8.9
In plain English
A high-severity resource allocation without limits in urllib3 from urllib3. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 54% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 4.0)8.9High
Exploit odds (30 days)0.7%top 45.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:8 | fence-agents-aliyun | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-aliyun | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-all | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-all | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-amt-ws | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-amt-ws | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-apc | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-apc | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-apc-snmp | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-apc-snmp | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-aws | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-aws | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-azure-arm | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-azure-arm | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-bladecenter | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-bladecenter | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-brocade | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-brocade | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-cisco-mds | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-cisco-mds | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-cisco-ucs | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-cisco-ucs | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-common | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-common | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-compute | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-compute | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-drac5 | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-drac5 | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-eaton-snmp | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-eaton-snmp | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-emerson | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-emerson | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-eps | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-eps | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-gce | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-gce | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-heuristics-ping | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-heuristics-ping | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-hpblade | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-hpblade | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-ibm-powervs | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-ibm-powervs | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-ibm-vpc | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-ibm-vpc | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-ibmblade | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-ibmblade | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-ifmib | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-ifmib | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-ilo-moonshot | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-ilo-moonshot | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-ilo-mp | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-ilo-mp | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-ilo-ssh | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-ilo-ssh | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-ilo2 | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-ilo2 | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-intelmodular | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-intelmodular | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-ipdu | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-ipdu | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-ipmilan | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-ipmilan | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-kdump | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-kdump | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-kubevirt | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-kubevirt | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-lpar | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-lpar | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-mpath | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-mpath | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-nutanix-ahv | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-nutanix-ahv | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-openstack | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-openstack | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-redfish | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-redfish | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-rhevm | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-rhevm | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-rsa | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-rsa | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-rsb | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-rsb | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-sbd | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-sbd | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-scsi | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-scsi | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-virsh | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-virsh | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-vmware-rest | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-vmware-rest | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-vmware-soap | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-vmware-soap | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-wti | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-wti | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:8 | fence-agents-zvm | 4.2.1-129.el8_10.20 | ALSA-2026:1240 |
| AlmaLinux:9 | fence-agents-zvm | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:9 | fence-virt | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:9 | fence-virtd | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:9 | fence-virtd-cpg | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:9 | fence-virtd-libvirt | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:9 | fence-virtd-multicast | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:9 | fence-virtd-serial | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:9 | fence-virtd-tcp | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:9 | ha-cloud-support | 4.10.0-98.el9_7.4 | ALSA-2026:1239 |
| AlmaLinux:10 | python3-urllib3 | 1.26.19-2.el10_1.1 | ALSA-2026:1086 |
| AlmaLinux:8 | python3-urllib3 | 1.24.2-9.el8_10 | ALSA-2026:1254 |
| AlmaLinux:9 | python3-urllib3 | 1.26.5-6.el9_7.1 | ALSA-2026:1087 |
| AlmaLinux:8 | python3.11-urllib3 | 1.26.12-6.el8_10 | ALSA-2026:1224 |
| AlmaLinux:9 | python3.11-urllib3 | 1.26.12-5.el9_7.1 | ALSA-2026:1089 |
| AlmaLinux:8 | python3.12-urllib3 | 1.26.19-2.el8_10 | ALSA-2026:1226 |
| AlmaLinux:9 | python3.12-urllib3 | 1.26.19-1.el9_7.1 | ALSA-2026:1088 |
| AlmaLinux:8 | resource-agents | 4.9.0-54.el8_10.27 | ALSA-2026:1241 |
| AlmaLinux:8 | resource-agents-aliyun | 4.9.0-54.el8_10.27 | ALSA-2026:1241 |
| AlmaLinux:8 | resource-agents-gcp | 4.9.0-54.el8_10.27 | ALSA-2026:1241 |
| AlmaLinux:8 | resource-agents-paf | 4.9.0-54.el8_10.27 | ALSA-2026:1241 |
| Alpine:v3.23 | py3-urllib3 | 2.6.3-r0 | ALPINE-CVE-2025-66418 |
| Debian:12 | python-urllib3 | 1.26.12-1+deb12u2 | DSA-6102-1 |
| Debian:12 | python-urllib3 | 1.26.12-1+deb12u2 | DEBIAN-CVE-2025-66418 |
| Debian:13 | python-urllib3 | 2.3.0-3+deb13u1 | DSA-6102-1 |
| Debian:13 | python-urllib3 | 2.3.0-3+deb13u1 | DEBIAN-CVE-2025-66418 |
| Debian:14 | python-urllib3 | 2.5.0-1.1 | DEBIAN-CVE-2025-66418 |
| PyPI | urllib3 | 2.6.0 | GHSA-gm62-xv2j-4w53 |
| PyPI | urllib3 | 2.6.0 | PYSEC-2026-1998 |
| Rocky Linux:8 | fence-agents | 0:4.2.1-129.el8_10.20 | RLSA-2026:1240 |
| Rocky Linux:9 | fence-agents | 0:4.10.0-98.el9_7.4 | RLSA-2026:1239 |
| Rocky Linux:10 | python-urllib3 | 0:1.26.19-2.el10_1.1 | RLSA-2026:1086 |
| Rocky Linux:8 | python-urllib3 | 0:1.24.2-9.el8_10 | RLSA-2026:1254 |
| Rocky Linux:9 | python-urllib3 | 0:1.26.5-6.el9_7.1 | RLSA-2026:1087 |
| Rocky Linux:8 | python3.11-urllib3 | 0:1.26.12-6.el8_10 | RLSA-2026:1224 |
| Rocky Linux:9 | python3.11-urllib3 | 0:1.26.12-5.el9_7.1 | RLSA-2026:1089 |
| Rocky Linux:8 | python3.12-urllib3 | 0:1.26.19-2.el8_10 | RLSA-2026:1226 |
| Rocky Linux:9 | python3.12-urllib3 | 0:1.26.19-1.el9_7.1 | RLSA-2026:1088 |
| Rocky Linux:8 | resource-agents | 0:4.9.0-54.el8_10.27 | RLSA-2026:1241 |
| Ubuntu:25.10 | python-pip | no fix listed | UBUNTU-CVE-2025-66418 |
| Ubuntu:26.10 | python-pip | no fix listed | UBUNTU-CVE-2025-66418 |
| Ubuntu:22.04:LTS | python-urllib3 | 1.26.5-1~exp1ubuntu0.4 | USN-7927-1 |
| Ubuntu:22.04:LTS | python-urllib3 | 1.26.5-1~exp1ubuntu0.4 | UBUNTU-CVE-2025-66418 |
| Ubuntu:24.04:LTS | python-urllib3 | 2.0.7-1ubuntu0.3 | UBUNTU-CVE-2025-66418 |
| Ubuntu:24.04:LTS | python-urllib3 | 2.0.7-1ubuntu0.3 | USN-7927-1 |
| Ubuntu:25.10 | python-urllib3 | 2.3.0-3ubuntu0.1 | USN-7927-1 |
| Ubuntu:25.10 | python-urllib3 | 2.3.0-3ubuntu0.1 | UBUNTU-CVE-2025-66418 |
| Ubuntu:26.04:LTS | python-urllib3 | 2.5.0-1ubuntu1 | UBUNTU-CVE-2025-66418 |
Affected products (as reported)
Weakness: CWE-770 · Vector: 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