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Vulnerability record · CVE-2021-3737 · published 4 March 2022

CVE-2021-3737: Python uncontrolled resource consumption vulnerability

Python · Python

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.

7.5 CVSS 3.1 High EPSS 12% · top 4.1% CWE-835 · CWE-835CWE-400 · Uncontrolled resource consumption
7.5CVSS 3.1 base score, v2 7.1
12%EPSS exploitation probability, 30 days
NoNot in CISA KEV
17Affected product versions listed by NVD
22References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

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

Affected products

17 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://bugs.python.org/issue44022 ExploitIssue TrackingVendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1995162 Issue TrackingPatchThird Party Advisory
https://github.com/python/cpython/pull/25916 PatchThird Party Advisory
https://github.com/python/cpython/pull/26503 PatchThird 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://python-security.readthedocs.io/vuln/urllib-100-continue-loop.html PatchThird Party Advisory
https://security.netapp.com/advisory/ntap-20220407-0009/ Third Party Advisory
https://ubuntu.com/security/CVE-2021-3737 PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpujul2022.html PatchThird Party Advisory
https://bugs.python.org/issue44022 ExploitIssue TrackingVendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1995162 Issue TrackingPatchThird Party Advisory
https://github.com/python/cpython/pull/25916 PatchThird Party Advisory
https://github.com/python/cpython/pull/26503 PatchThird 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 PatchThird Party Advisory
https://security.netapp.com/advisory/ntap-20220407-0009/ Third Party Advisory
https://ubuntu.com/security/CVE-2021-3737 PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpujul2022.html PatchThird Party Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2021-3737), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.