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.

Project Subscriptions

Vendors Products
Fedoraproject Subscribe
Extra Packages For Enterprise Linux Subscribe
Hci Compute Node Firmware Subscribe
Management Services For Element Software And Netapp Hci Subscribe
Ontap Select Deploy Administration Utility Subscribe
Solidfire\, Enterprise Sds \& Hci Storage Node Subscribe
Codeready Linux Builder Subscribe
Codeready Linux Builder For Ibm Z Systems Subscribe
Codeready Linux Builder For Power Little Endian Subscribe
Enterprise Linux Subscribe
Enterprise Linux Eus Subscribe
Enterprise Linux For Ibm Z Systems Subscribe
Enterprise Linux For Ibm Z Systems Eus Subscribe
Enterprise Linux For Power Little Endian Subscribe
Enterprise Linux For Power Little Endian Eus Subscribe
Enterprise Linux Server Aus Subscribe
Enterprise Linux Server For Power Little Endian Update Services For Sap Solutions Subscribe
Enterprise Linux Server Tus Subscribe
Enterprise Linux Server Update Services For Sap Solutions Subscribe
Rhel Software Collections Subscribe
Advisories
Source ID Title
Debian DLA Debian DLA DLA-2808-1 python3.5 security update
Debian DLA Debian DLA DLA-3432-1 python2.7 security update
Debian DLA Debian DLA DLA-3477-1 python3.7 security update
Debian DLA Debian DLA DLA-3980-1 python3.9 security update
EUVD EUVD EUVD-2021-27010 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.
Ubuntu USN Ubuntu USN USN-5083-1 Python vulnerabilities
Ubuntu USN Ubuntu USN USN-5199-1 Python vulnerabilities
Ubuntu USN Ubuntu USN USN-5200-1 Python vulnerabilities
Ubuntu USN Ubuntu USN USN-6891-1 Python vulnerabilities
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Mon, 03 Nov 2025 22:30:00 +0000

Type Values Removed Values Added
References

Projects

Sign in to view the affected projects.

cve-icon MITRE

Status: PUBLISHED

Assigner: redhat

Published:

Updated: 2025-11-03T21:45:06.299Z

Reserved: 2021-08-23T00:00:00.000Z

Link: CVE-2021-3733

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Modified

Published: 2022-03-10T17:42:59.623

Modified: 2025-11-03T22:15:50.833

Link: CVE-2021-3733

cve-icon Redhat

Severity : Moderate

Publid Date: 2021-08-10T00:00:00Z

Links: CVE-2021-3733 - Bugzilla

cve-icon OpenCVE Enrichment

No data.

Weaknesses