CVE-2025-66418
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.
Scoring
- Severity
- HIGH
- CVSS base score
- 8.9
- CVSS 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
- EPSS probability
- 0.68%
- CWE
- CWE-770
- Published
- 2025-12-05
- Last modified
- 2026-03-13
Affected products
- urllib3 urllib3
Weakness type
Related vulnerabilities
- CVE-2026-87908 — multiparty vulnerable to Denial of Service via unbounded part-header accumulation
- CVE-2026-45769 — ikev2: unbounded client transform storage can lead to resource exhaustion
- CVE-2026-45768 — Suricata ldap: unbounded responses per transaction can lead to resource exhaustion
- CVE-2026-45766 — Suricata nfs: unbounded stateful structures can lead to resource exhaustion
- CVE-2026-45765 — Suricata dnp3: unbounded reassembly can lead to resource exhaustion
- CVE-2026-88012 — Traefik: respondingTimeouts.readTimeout is not applied to HTTP/3, leaving slow-body uploads unbounded
- CVE-2026-45763 — Suricata lua: sandbox allocation limit not enforced for new allocations
- CVE-2026-88878 — Traefik v2.8.2 through v3.6 HTTP/3 Timeout Bypass