urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.
History

Tue, 13 Oct 2026 20:30:00 +0000

Type Values Removed Values Added
First Time appeared Python
Python urllib3
CPEs cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:*
Vendors & Products Python
Python urllib3

Wed, 30 Sep 2026 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Important


Tue, 29 Sep 2026 17:30:00 +0000

Type Values Removed Values Added
First Time appeared Urllib3
Urllib3 urllib3
Vendors & Products Urllib3
Urllib3 urllib3
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Tue, 29 Sep 2026 15:45:00 +0000

Type Values Removed Values Added
Description urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.
Title urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory
Weaknesses CWE-770
References
Metrics cvssV4_0

{'score': 8.9, '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'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2026-09-29T15:36:05.963Z

Updated: 2026-09-29T16:23:23.167Z

Reserved: 2026-09-24T21:43:37.208Z

Link: CVE-2026-97689

cve-icon Vulnrichment

Updated: 2026-09-29T16:23:05.435Z

cve-icon NVD

Status : Analyzed

Published: 2026-09-29T16:17:18.837

Modified: 2026-10-13T20:20:06.950

Link: CVE-2026-97689

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-29T15:36:05Z

Links: CVE-2026-97689 - Bugzilla