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.
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

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.