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Fencer Vulns
medium 6.5

CVE-2021-3733 json

There's a flaw in urllib's AbstractBasicAuthHandler class.

published 2022-03-07 4 y ago modified 2026-10-14 25 d ago also BIT-libpython-2021-3733 , BIT-python-2021-3733 , BIT-python-min-2021-3733 , EUVD-2021-27010

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
4.8%
EPSS 4.8% chance of exploitation in 30 days, percentile 92%
public exploits
0
none known

Summary

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.

Patch / fix

  • bitnami libpython 3.6.14, 3.7.11, 3.8.10, 3.9.5
  • bitnami python 3.6.14, 3.7.11, 3.8.10, 3.9.5
  • bitnami python-min 3.6.14, 3.7.11, 3.8.10, 3.9.5, 3.10.1
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • pypy3 Debian 14, Debian 13, Debian 12 7.3.5+dfsg-2

debian advisories DEBIAN-CVE-2021-3733

  • python3.6 Ubuntu 18.04 LTS 3.6.9-1~18.04ubuntu1.6
  • python3.7 Ubuntu 18.04 LTS 3.7.5-2ubuntu1~18.04.2
  • python3.8 Ubuntu 18.04 LTS 3.8.0-3ubuntu1~18.04.2
  • python3.8 Ubuntu 20.04 LTS 3.8.10-0ubuntu1~20.04
  • python3.9 Ubuntu 20.04 LTS 3.9.5-3~20.04.1
  • python3.4 Ubuntu Pro 14.04 LTS 3.4.3-1ubuntu1~14.04.7+esm11
  • python3.5 Ubuntu Pro 14.04 LTS 3.5.2-2ubuntu0~16.04.4~14.04.1+esm1
  • python3.5 Ubuntu Pro 16.04 LTS 3.5.2-2ubuntu0~16.04.13+esm1

ubuntu advisories UBUNTU-CVE-2021-3733

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • rh-python38-babel RHEL 3 SOFTWARE_COLLECTIONS 2.7.0-12.el7
  • rh-python38-python RHEL 3 SOFTWARE_COLLECTIONS 3.8.11-2.el7
  • rh-python38-python-pip RHEL 3 SOFTWARE_COLLECTIONS 19.3.1-2.el7
  • rh-python38-python-idle RHEL 3 SOFTWARE_COLLECTIONS 3.8.11-2.el7
  • rh-python38-python-libs RHEL 3 SOFTWARE_COLLECTIONS 3.8.11-2.el7
  • rh-python38-python-lxml RHEL 3 SOFTWARE_COLLECTIONS 4.4.1-7.el7
  • rh-python38-python-test RHEL 3 SOFTWARE_COLLECTIONS 3.8.11-2.el7
  • rh-python38-python-babel RHEL 3 SOFTWARE_COLLECTIONS 2.7.0-12.el7

red hat advisories RHSA-2021:3254RHSA-2021:4160RHSA-2022:1821RHSA-2022:1663RHSA-2022:1764RHSA-2021:4057

  • python39 SLE Module for Basesystem 15 SP3, openSUSE Leap 15.4, openSUSE Leap 15.3 3.9.10-150300.4.8.2
  • python39-core SLE Module for Development Tools 15 SP3, SLE Module for Basesystem 15 SP3, openSUSE Leap 15.4 +1 more 3.9.10-150300.4.8.1
  • python39-documentation openSUSE Leap 15.4, openSUSE Leap 15.3 3.9.10-150300.4.8.1
  • python3 SLES 15 SP1-BCL, SLE Module for Basesystem 15 SP2, SLE Micro 5.1 +10 more 3.6.15-3.91.4
  • python3-core SLES 15 SP1-BCL, SLE Module for Development Tools 15 SP2, SLE Module for Basesystem 15 SP2 +11 more 3.6.15-3.91.3
  • python3 SLE Module for Basesystem 15 SP3 3.6.15-10.9.1
  • python3-core SLE Module for Development Tools 15 SP3, SLE Module for Basesystem 15 SP3 3.6.15-10.9.1
  • python SLES for SAP 12 SP5, SLES 12 SP5 2.7.18-28.74.1

suse advisories SUSE-SU-2022:1485-1SUSE-SU-2021:4015-2SUSE-SU-2021:4104-1SUSE-SU-2021:4015-1SUSE-SU-2021:3524-1SUSE-SU-2021:3489-1

  • python openSUSE Tumbleweed 2.7.18-8.1
  • python36 openSUSE Tumbleweed 3.6.15-1.1
  • python39 openSUSE Tumbleweed 3.9.7-2.1
  • python3 openSUSE Leap 15.3 3.6.15-10.9.1
  • python3-core openSUSE Leap 15.3 3.6.15-10.9.1
  • python3-documentation openSUSE Leap 15.3 3.6.15-10.9.1
  • python openSUSE Leap 15.2 2.7.18-lp152.3.21.1
  • python-base openSUSE Leap 15.2 2.7.18-lp152.3.21.1

opensuse advisories openSUSE-SU-2024:11202-1openSUSE-SU-2024:11284-1openSUSE-SU-2024:11286-1openSUSE-SU-2021:4104-1openSUSE-SU-2021:1418-1openSUSE-SU-2021:3489-1

  • babel AlmaLinux 8 2.5.1-10.module_el8.6.0+2781+fed64c13
  • python2 AlmaLinux 8 2.7.18-10.module_el8.6.0+2781+fed64c13.alma
  • python2-py AlmaLinux 8 1.5.3-6.module_el8.6.0+2781+fed64c13
  • python2-dns AlmaLinux 8 1.15.0-10.module_el8.6.0+2781+fed64c13
  • python2-pip AlmaLinux 8 9.0.3-19.module_el8.6.0+2781+fed64c13
  • python2-six AlmaLinux 8 1.11.0-6.module_el8.6.0+2781+fed64c13
  • python2-bson AlmaLinux 8 3.7.0-1.module_el8.6.0+2781+fed64c13
  • python2-idna AlmaLinux 8 2.5-7.module_el8.6.0+2781+fed64c13

almalinux advisories ALSA-2022:1821ALSA-2022:1764ALSA-2021:4160

  • pytz Rocky Linux 8 2017.2-12.module+el8.5.0+706+735ec4b3
  • pytz Rocky Linux 8 2017.2-12.module+el8.4.0+403+9ae17a31
  • babel Rocky Linux 8 2.5.1-10.module+el8.5.0+706+735ec4b3
  • numpy Rocky Linux 8 1:1.14.2-16.module+el8.5.0+706+735ec4b3
  • numpy Rocky Linux 8 1:1.14.2-16.module+el8.4.0+403+9ae17a31
  • scipy Rocky Linux 8 1.0.0-21.module+el8.5.0+671+195e4563
  • Cython Rocky Linux 8 0.28.1-7.module+el8.5.0+706+735ec4b3
  • Cython Rocky Linux 8 0.28.1-7.module+el8.4.0+403+9ae17a31

rocky linux advisories RLSA-2022:1821RLSA-2022:1764RLSA-2021:4160

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3733 updated cvss 6.5

python: urllib: Regular expression DoS in AbstractBasicAuthHandler

  • Red Hat Enterprise Linux 6 python, tkinter, python-libs, python-test, python-tools Red Hat Enterprise Linux 7 python, python3, tkinter, python-libs, python-test, python-tools, +4 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 scipy, python36, python-nose, python-wheel, python3-bson, python3-nose, +19 more
    affected: no fix available
  • Red Hat CodeReady Linux Builder (v. 8) pytest 6.0.2-2.module+el8.4.0+9822+20bf1249, Cython 0.29.21-5.module+el8.4.0+9822+20bf1249, pybind11 2.6.1-2.module+el8.4.0+9822+20bf1249, python-py 1.10.0-1.module+el8.4.0+9822+20bf1249, python39-py 1.10.0-1.module+el8.4.0+9822+20bf1249, python-attrs 20.3.0-2.module+el8.4.0+9822+20bf1249, +16 more
    fixed: vendor fix RHSA-2021:4160
  • Red Hat Enterprise Linux AppStream (v. 8) python3-idle 3.6.8-39.el8_4, python3-test 3.6.8-39.el8_4, platform-python 3.6.8-39.el8_4, python3-tkinter 3.6.8-39.el8_4, pytz 2019.3-3.module+el8.4.0+8888+89bc7e79, scipy 1.3.1-4.module+el8.4.0+8888+89bc7e79, +207 more Red Hat Enterprise Linux BaseOS (v. 8) python3 3.6.8-39.el8_4, python3-libs 3.6.8-39.el8_4, python3-test 3.6.8-39.el8_4, platform-python 3.6.8-39.el8_4
    fixed: vendor fix RHSA-2021:4057
  • Red Hat Enterprise Linux CRB (v. 8) pytest 4.6.6-3.module+el8.4.0+8888+89bc7e79, python-py 1.8.0-8.module+el8.4.0+8888+89bc7e79, python38-py 1.8.0-8.module+el8.4.0+8888+89bc7e79, python-attrs 19.3.0-3.module+el8.4.0+8888+89bc7e79, python-pluggy 0.13.0-3.module+el8.4.0+8888+89bc7e79, python-packaging 19.2-3.module+el8.4.0+8888+89bc7e79, +12 more
    fixed: vendor fix RHSA-2022:1764
  • Red Hat Software Collections for Red Hat Enterprise Linux Server (v. 7) rh-python38-babel 2.7.0-12.el7, rh-python38-python 3.8.11-2.el7, rh-python38-python-lxml 4.4.1-7.el7, rh-python38-python-pip 19.3.1-2.el7, rh-python38-python-idle 3.8.11-2.el7, rh-python38-python-libs 3.8.11-2.el7, +9 more Red Hat Software Collections for Red Hat Enterprise Linux Server EUS (v. 7.7) rh-python38-babel 2.7.0-12.el7, rh-python38-python 3.8.11-2.el7, rh-python38-python-lxml 4.4.1-7.el7, rh-python38-python-pip 19.3.1-2.el7, rh-python38-python-idle 3.8.11-2.el7, rh-python38-python-libs 3.8.11-2.el7, +9 more Red Hat Software Collections for Red Hat Enterprise Linux Workstation (v. 7) rh-python38-babel 2.7.0-12.el7, rh-python38-python 3.8.11-2.el7, rh-python38-python-lxml 4.4.1-7.el7, rh-python38-python-pip 19.3.1-2.el7, rh-python38-python-idle 3.8.11-2.el7, rh-python38-python-libs 3.8.11-2.el7, +9 more
    fixed: vendor fix RHSA-2021:3254
  • Red Hat Software Collections for RHEL Workstation(v. 7) python27-python 2.7.18-4.el7, python27-tkinter 2.7.18-4.el7, python27-python-libs 2.7.18-4.el7, python27-python-test 2.7.18-4.el7, python27-python-tools 2.7.18-4.el7 Red Hat Software Collections for RHEL(v. 7) python27-python 2.7.18-4.el7, python27-tkinter 2.7.18-4.el7, python27-python-libs 2.7.18-4.el7, python27-python-test 2.7.18-4.el7, python27-python-tools 2.7.18-4.el7
    fixed: vendor fix RHSA-2022:1663
  • Red Hat Software Collections for RHEL Workstation(v. 7) python27-python-pip 8.1.2-7.el7 Red Hat Software Collections for RHEL(v. 7) python27-python-pip 8.1.2-7.el7
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-23-348-10 updated cvss 6.5

Siemens SIMATIC S7-1500

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.0, < 3.1.5
    affected: fixed in V3.1.5, mitigation support.industry.siemens.com

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
31 d ago

Exploit prediction

4.80% chance of exploitation in the next 30 days, higher than 92% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugs.python.org https://bugs.python.org/issue43075 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:N/I:N/A:P
OSV 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
bitnami libpython
<3.6.14
>=3.7.0, <3.7.11
>=3.8.0, <3.8.10
>=3.9.0, <3.9.5
3.6.14
3.7.11
3.8.10
3.9.5
bitnami python
<3.6.14
>=3.7.0, <3.7.11
>=3.8.0, <3.8.10
>=3.9.0, <3.9.5
3.6.14
3.7.11
3.8.10
3.9.5
bitnami python-min
<3.6.14
>=3.7.0, <3.7.11
>=3.8.0, <3.8.10
>=3.9.0, <3.9.5
>=3.10.0, <3.10.1
3.6.14
3.7.11
3.8.10
3.9.5
3.10.1

Affected products

  • n/a python
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.