Reference page — cumulative record through Monday, October 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2021-3737

CVE-2021-3737HIGH

n/a python — A flaw was found in python.

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   N   L   N   N  U  N  N  H    7.5   .1317   96.3     —

AFFECTED
  Product  Versions                                                                                    Fixed
  python   Fixed in python v3.6.14, python v3.7.11, python v3.8.11, python v3.9.6, python v3.10.0b2 –  —

TIMELINE
  Aug 26  Reserved by redhat
  Mar 4   Published (CNA: redhat)
  Oct 14  EXPLOIT PUBLISHED — CVE-2021-3737 (python). Public exploit reference added.

CWE-400, CWE-835 · CNA: redhat · CVSS v3.1 · 13 references · NVD status: Modified

Description

A flaw was found in python. An improperly handled HTTP response in the HTTP client code of python may allow a remote attacker, who controls the HTTP server, to make the client script enter an infinite loop, consuming CPU time. The highest threat from this vulnerability is to system availability.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
August 26, 2021	Reserved	Reserved by redhat
March 4, 2022	Published	Published (CNA: redhat)
October 14, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2021-3737 (python). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
n/a	python	—	Fixed in python v3.6.14, python v3.7.11, python v3.8.11, python v3.9.6, python v3.10.0b2	—

Weaknesses

CWE-400 · CWE-835

References (13)

https://bugs.python.org/issue44022 [Exploit, Issue Tracking, Vendor Advisory]
https://bugzilla.redhat.com/show_bug.cgi?id=1995162 [Issue Tracking, Patch, Third Party Advisory]
https://cert-portal.siemens.com/productcert/html/ssa-398330.html
https://github.com/python/cpython/pull/25916 [Patch, Third Party Advisory]
https://github.com/python/cpython/pull/26503 [Patch, Third Party Advisory]
https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html
https://lists.debian.org/debian-lts-announce/2023/06/msg00039.html
https://lists.debian.org/debian-lts-announce/2024/11/msg00024.html
https://lists.debian.org/debian-lts-announce/2024/12/msg00000.html
https://python-security.readthedocs.io/vuln/urllib-100-continue-loop.html [Patch, Third Party Advisory]
https://security.netapp.com/advisory/ntap-20220407-0009/ [Third Party Advisory]
https://ubuntu.com/security/CVE-2021-3737 [Patch, Third Party Advisory]
https://www.oracle.com/security-alerts/cpujul2022.html [Patch, Third Party Advisory]

Authoritative record: CVE-2021-3737 at cve.org

Weaknesses: CWE-400 · CWE-835

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2021-3737 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Monday, October 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.