What’s Vulnerable › Vulnerabilities
CVE-2021-3733
- Severity: medium (CVSS 6.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 4.8% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2022-03-10 · updated 2026-10-14
- Weakness: CWE-400
Description
There's a flaw in urllib's AbstractBasicAuthHandler class. An attacker who controls a malicious HTTP server that an HTTP client (such as web browser) connects to, could trigger a Regular Expression Denial of Service (ReDOS) during an authentication request with a specially crafted payload that is sent by the server to the client. The greatest threat that this flaw poses is to application availability.
Affected products
- Fedoraproject Extra Packages For Enterprise Linux: 7.0
- Fedoraproject Fedora: 33, 34, 35, 36
- NetApp Hci Compute Node Firmware: all versions
- NetApp Management Services For Element Software And Netapp Hci: all versions
- NetApp ONTAP Select Deploy administration utility: all versions
- NetApp Solidfire, Enterprise Sds & Hci Storage Node: all versions
- Python: before 3.6.14; from 3.7.0 before 3.7.11; from 3.8.0 before 3.8.10; from 3.9.0 before 3.9.5; 3.10.0 — fixed in 3.6.14, 3.7.11, 3.8.10, 3.9.5
- RedHat Codeready Linux Builder: 8.0
- RedHat Codeready Linux Builder For Ibm Z Systems: 8.0
- RedHat Codeready Linux Builder For Power Little Endian: 8.0
- Red Hat Enterprise Linux: 8.0
- RedHat Enterprise Linux Eus: 8.4
- RedHat Enterprise Linux For Ibm Z Systems: 8.0
- RedHat Enterprise Linux For Ibm Z Systems Eus: 8.4
- RedHat Enterprise Linux For Power Little Endian: 8.0
- RedHat Enterprise Linux For Power Little Endian Eus: 8.4
- RedHat Enterprise Linux Server Aus: 8.4
- RedHat Enterprise Linux Server For Power Little Endian Update Services For Sap Solutions: 8.4
- RedHat Enterprise Linux Server Tus: 8.4
- RedHat Enterprise Linux Server Update Services For Sap Solutions: 8.4
How to fix
Upgrade to a fixed version: Python 3.6.14, 3.7.11, 3.8.10, 3.9.5. Check the vendor advisory for mitigations.
References
- https://bugs.python.org/issue43075
- https://bugzilla.redhat.com/show_bug.cgi?id=1995234
- https://github.com/python/cpython/commit/7215d1ae25525c92b026166f9d5cac85fb
- https://github.com/python/cpython/pull/24391
- https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html
- https://lists.debian.org/debian-lts-announce/2023/06/msg00039.html
- https://security.netapp.com/advisory/ntap-20220407-0001/
- https://ubuntu.com/security/CVE-2021-3733
- https://bugs.python.org/issue43075
- https://bugzilla.redhat.com/show_bug.cgi?id=1995234
- https://github.com/python/cpython/commit/7215d1ae25525c92b026166f9d5cac85fb
- https://github.com/python/cpython/pull/24391
Get alerted when CVE-2021-3733 or the next vulnerability affects your stack