{"id":"CVE-2021-3737","title":"A flaw was found in python","summary":"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 highes…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cwe":["CWE-835","CWE-400","CWE-835"],"vendor":"python","product":"python","affected":["python >= 3.6.0, < 3.6.14","python >= 3.7.0, < 3.7.11","python >= 3.8.0, < 3.8.11","python >= 3.9.0, < 3.9.6","codeready_linux_builder = 8.0","codeready_linux_builder_for_ibm_z_systems = 8.0","codeready_linux_builder_for_power_little_endian = 8.0","enterprise_linux = 6.0","enterprise_linux = 7.0","enterprise_linux = 8.0","enterprise_linux_for_ibm_z_systems = 8.0","enterprise_linux_for_power_little_endian = 8.0","fedora = 33","fedora = 34","ubuntu_linux = 14.04","ubuntu_linux = 16.04","ubuntu_linux = 18.04","ubuntu_linux = 20.04","ubuntu_linux = 21.04","hci","management_services_for_element_software","netapp_xcp_smb","ontap_select_deploy_administration_utility","xcp_nfs","communications_cloud_native_core_binding_support_function = 22.1.3","communications_cloud_native_core_network_exposure_function = 22.1.1","communications_cloud_native_core_policy = 22.2.0"],"patched":["python 3.9.6"],"published":"2022-03-04","updated":"2026-10-14","sourceUpdated":"2026-10-14T10:17:47.917","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2021-3737","references":[{"url":"https://bugs.python.org/issue44022","label":"secalert@redhat.com"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1995162","label":"secalert@redhat.com"},{"url":"https://github.com/python/cpython/pull/25916","label":"secalert@redhat.com"},{"url":"https://github.com/python/cpython/pull/26503","label":"secalert@redhat.com"},{"url":"https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html","label":"secalert@redhat.com"},{"url":"https://lists.debian.org/debian-lts-announce/2023/06/msg00039.html","label":"secalert@redhat.com"},{"url":"https://python-security.readthedocs.io/vuln/urllib-100-continue-loop.html","label":"secalert@redhat.com"},{"url":"https://security.netapp.com/advisory/ntap-20220407-0009/","label":"secalert@redhat.com"},{"url":"https://ubuntu.com/security/CVE-2021-3737","label":"secalert@redhat.com"},{"url":"https://www.oracle.com/security-alerts/cpujul2022.html","label":"secalert@redhat.com"},{"url":"https://bugs.python.org/issue44022","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1995162","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/python/cpython/pull/25916","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/python/cpython/pull/26503","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.debian.org/debian-lts-announce/2023/06/msg00039.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.debian.org/debian-lts-announce/2024/11/msg00024.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.debian.org/debian-lts-announce/2024/12/msg00000.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://python-security.readthedocs.io/vuln/urllib-100-continue-loop.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://security.netapp.com/advisory/ntap-20220407-0009/","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://ubuntu.com/security/CVE-2021-3737","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.oracle.com/security-alerts/cpujul2022.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-398330.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}],"tags":["nvd"],"epss":0.11586,"epssPercentile":0.95961,"ingestedAt":"2026-10-14T10:25:41.192Z","slug":"CVE-2021-3737","body":"## Overview\n\nA 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.\n\n## Affected\n\n- `python >= 3.6.0, < 3.6.14`\n- `python >= 3.7.0, < 3.7.11`\n- `python >= 3.8.0, < 3.8.11`\n- `python >= 3.9.0, < 3.9.6`\n- `codeready_linux_builder = 8.0`\n- `codeready_linux_builder_for_ibm_z_systems = 8.0`\n- `codeready_linux_builder_for_power_little_endian = 8.0`\n- `enterprise_linux = 6.0`\n- `enterprise_linux = 7.0`\n- `enterprise_linux = 8.0`\n- `enterprise_linux_for_ibm_z_systems = 8.0`\n- `enterprise_linux_for_power_little_endian = 8.0`\n- `fedora = 33`\n- `fedora = 34`\n- `ubuntu_linux = 14.04`\n- `ubuntu_linux = 16.04`\n- `ubuntu_linux = 18.04`\n- `ubuntu_linux = 20.04`\n- `ubuntu_linux = 21.04`\n- `hci`\n- `management_services_for_element_software`\n- `netapp_xcp_smb`\n- `ontap_select_deploy_administration_utility`\n- `xcp_nfs`\n- `communications_cloud_native_core_binding_support_function = 22.1.3`\n- `communications_cloud_native_core_network_exposure_function = 22.1.1`\n- `communications_cloud_native_core_policy = 22.2.0`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `python 3.9.6`","depth":"twilight","depthScore":44,"depthScoreParts":{"impact":41.3,"likelihood":2.3,"exploitation":0,"ransomware":0},"changes":[]}