CVE-2026-97689

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.

CVSS 4.0

8.9CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

CVSS 3.1

7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

0.3% chance of exploitation in the next 30 days; higher than 26% of CVEs (scores of 2026-10-25)

CWE

CWE-770

Published

2026-09-29

Modified

2026-10-13

Record from

the NVD, synced 2026-10-19

Affected

• python:urllib3

Packages (OSV)

References

• https://github.com/urllib3/urllib3/commit/cd770b059b543be29298ea5c52afb0b1b090f5ed
• https://github.com/urllib3/urllib3/releases/tag/2.8.0
• https://github.com/urllib3/urllib3/security/advisories/GHSA-vxq7-64xx-v4gw

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