HOMEVULNERABILITIESCVE-2021-3733
MEDIUM

CVE-2021-3733

CWE-400Published: March 10, 2022· Updated: Jun 17, 2026

6.5
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-3733 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

Exploitation requires low privileges, which limits the exposure to scenarios where an attacker has already gained initial access.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 6.5.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.Low
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected Vendors & Products

Fedora2 product(s)
extra packages for enterprise linuxfedora
netapp4 product(s)
management services for element software and netapp hciontap select deploy administration utilitysolidfire\, enterprise sds \& hci storage nodehci compute node firmware
Python1 product(s)
python
Red Hat13 product(s)
codeready linux buildercodeready linux builder for ibm z systemscodeready linux builder for power little endianenterprise linuxenterprise linux eusenterprise linux for ibm z systemsenterprise linux for ibm z systems eusenterprise linux for power little endianenterprise linux for power little endian eusenterprise linux server ausenterprise linux server for power little endian update services for sap solutionsenterprise linux server tus+1
Source: NVD CPE · 24 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://bugs.python.org/issue43075
PATCHhttps://github.com/python/cpython/commit/7215d1ae25525c92b026166f9d5cac85fb
PATCHhttps://github.com/python/cpython/pull/24391
PATCHhttps://ubuntu.com/security/CVE-2021-3733
PATCHhttps://bugs.python.org/issue43075
PATCHhttps://github.com/python/cpython/commit/7215d1ae25525c92b026166f9d5cac85fb
PATCHhttps://github.com/python/cpython/pull/24391
PATCHhttps://ubuntu.com/security/CVE-2021-3733
ADVISORYhttps://bugzilla.redhat.com/show_bug.cgi?id=1995234
ADVISORYhttps://security.netapp.com/advisory/ntap-20220407-0001/
ADVISORYhttps://bugzilla.redhat.com/show_bug.cgi?id=1995234
ADVISORYhttps://security.netapp.com/advisory/ntap-20220407-0001/

All References (17)

→
https://bugs.python.org/issue43075Exploit · Issue Tracking · Patch · Vendor Advisory
→
https://bugzilla.redhat.com/show_bug.cgi?id=1995234Issue Tracking · Third Party Advisory
→
https://github.com/python/cpython/commit/7215d1ae25525c92b026166f9d5cac85fbPatch · Third Party Advisory
→
https://github.com/python/cpython/pull/24391Patch · Third 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://security.netapp.com/advisory/ntap-20220407-0001/Third Party Advisory
→
https://ubuntu.com/security/CVE-2021-3733Patch · Third Party Advisory
→
https://bugs.python.org/issue43075Exploit · Issue Tracking · Patch · Vendor Advisory
→
https://bugzilla.redhat.com/show_bug.cgi?id=1995234Issue Tracking · Third Party Advisory
→
https://github.com/python/cpython/commit/7215d1ae25525c92b026166f9d5cac85fbPatch · Third Party Advisory
→
https://github.com/python/cpython/pull/24391Patch · Third 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/2024/12/msg00000.html

Quick Facts

CVE IDCVE-2021-3733
CVSS Score6.5 / 10
SeverityMEDIUM
WeaknessCWE-400
CISA KEVNo
Affected4 vendor(s)
PublishedMar 10, 2022

Related CVEs (CWE-400)

CVE-2024-39462
9.8
CVE-2025-43193
9.8
CVE-2015-4412
9.8
CVE-2019-10952
9.8
CVE-2024-45166
9.8
CVE-2025-61303
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-3733 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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