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Fencer Intel
critical 9.8

CVE-2021-29921 json

In Python before 3,9,5, the ipaddress library mishandles leading zero characters in the octets of an IP address string.

published 5y ago modified last mo. also BIT-libpython-2021-29921 , BIT-python-2021-29921 , BIT-python-min-2021-29921 , EUVD-2021-16395

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
6.8%
EPSS 6.8% chance of exploitation in 30 days, percentile 94%
public exploits
0
none known

Summary

In Python before 3,9,5, the ipaddress library mishandles leading zero characters in the octets of an IP address string. This (in some situations) allows attackers to bypass access control that is based on IP addresses.

Patch / fix

  • bitnami libpython 3.8.12, 3.9.5
  • bitnami python 3.8.12, 3.9.5
  • bitnami python-min 3.8.12, 3.9.5
  • python python 3.8.12, 3.9.5
  • pypy3 Debian 14, Debian 13, Debian 12 7.3.8+dfsg-1

debian advisories DEBIAN-CVE-2021-29921

  • python3.8 Ubuntu 20.04 LTS 3.8.10-0ubuntu1~20.04.1
  • python3.9 Ubuntu 20.04 LTS 3.9.5-3~20.04.1
  • python3.8 Ubuntu Pro 18.04 LTS 3.8.0-3ubuntu1~18.04.2+esm2

ubuntu advisories UBUNTU-CVE-2021-29921

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

  • pytz RHEL 8 2019.3-3.module+el8.4.0+8888+89bc7e79
  • babel RHEL 8 2.7.0-11.module+el8.5.0+11015+9c1c7c42
  • numpy RHEL 8 1.17.3-6.module+el8.5.0+12205+a865257a
  • scipy RHEL 8 1.3.1-4.module+el8.4.0+8888+89bc7e79
  • Cython RHEL 8 0.29.14-4.module+el8.4.0+8888+89bc7e79
  • pytest RHEL 8 4.6.6-3.module+el8.4.0+8888+89bc7e79
  • PyYAML RHEL 8 5.4.1-1.module+el8.5.0+10721+14d8e0d5
  • mod_wsgi RHEL 8 4.6.8-3.module+el8.4.0+8888+89bc7e79

red hat advisories RHSA-2021:4162RHSA-2021:3254RHSA-2021:4160

  • python39 SLE Module for Basesystem 15 SP3 3.9.6-4.3.4
  • python39-core SLE Module for Development Tools 15 SP3, SLE Module for Basesystem 15 SP3 3.9.6-4.3.3

suse advisories SUSE-SU-2021:2940-1

  • python39 openSUSE Tumbleweed 3.9.7-2.1

opensuse advisories openSUSE-SU-2024:11286-1

  • python38-py AlmaLinux 8 1.8.0-8.module_el8.6.0+2778+cd494b30
  • python38-ply AlmaLinux 8 3.11-10.module_el8.6.0+2778+cd494b30
  • python38-six AlmaLinux 8 1.12.0-10.module_el8.6.0+2778+cd494b30
  • python38-cffi AlmaLinux 8 1.13.2-3.module_el8.6.0+2778+cd494b30
  • python38-idna AlmaLinux 8 2.8-6.module_el8.6.0+2778+cd494b30
  • python38-pytz AlmaLinux 8 2019.3-3.module_el8.6.0+2778+cd494b30
  • python38-attrs AlmaLinux 8 19.3.0-3.module_el8.6.0+2778+cd494b30
  • python38-babel AlmaLinux 8 2.7.0-11.module_el8.6.0+2778+cd494b30

almalinux advisories ALSA-2021:4162ALSA-2021:4160

  • pytz Rocky Linux 8 2019.3-3.module+el8.4.0+570+c2eaf144
  • babel Rocky Linux 8 2.7.0-11.module+el8.5.0+672+ab6eb015
  • numpy Rocky Linux 8 1.17.3-6.module+el8.5.0+672+ab6eb015
  • scipy Rocky Linux 8 1.3.1-4.module+el8.5.0+672+ab6eb015
  • scipy Rocky Linux 8 1.3.1-4.module+el8.4.0+570+c2eaf144
  • Cython Rocky Linux 8 0.29.14-4.module+el8.4.0+570+c2eaf144
  • pytest Rocky Linux 8 4.6.6-3.module+el8.4.0+570+c2eaf144
  • PyYAML Rocky Linux 8 5.4.1-1.module+el8.5.0+672+ab6eb015

rocky linux advisories RLSA-2021:4162RLSA-2021:4160

  • python3 Alpine 3.24, Alpine 3.23, Alpine 3.22 +7 more 3.9.5-r0

alpine advisories ALPINE-CVE-2021-29921

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • python Arch Linux 3.9.5-1

arch linux advisories AVG-1913

Is CVE-2021-29921 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

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-2021-29921 updated cvss 9.1

python-ipaddress: Improper input validation of octal strings

  • Red Hat CodeReady Linux Builder (v. 8) pytest 4.6.6-3.module+el8.4.0+8888+89bc7e79, 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 1.8.0-8.module+el8.4.0+8888+89bc7e79, python-py 1.10.0-1.module+el8.4.0+9822+20bf1249, +34 more Red Hat Enterprise Linux AppStream (v. 8) pytz 2019.3-3.module+el8.4.0+8888+89bc7e79, scipy 1.3.1-4.module+el8.4.0+8888+89bc7e79, scipy 1.5.4-3.module+el8.4.0+9822+20bf1249, babel 2.7.0-11.module+el8.5.0+11015+9c1c7c42, numpy 1.17.3-6.module+el8.5.0+12205+a865257a, numpy 1.19.4-3.module+el8.5.0+12204+54860423, +114 more
    fixed: vendor fix RHSA-2021:4162
  • 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 Enterprise Linux 7 python-pip, python3-pip, python-ipaddress Red Hat Enterprise Linux 8 scipy, python36, python-nose, python-wheel, python3-bson, python3-nose, +21 more Red Hat Software Collections rh-python36-python, python27-python-pip, rh-python36-python-libs, rh-python36-python-test, rh-python36-python-tools, rh-python36-python-tkinter
    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 SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
last mo.

Exploit prediction

6.76% chance of exploitation in the next 30 days, higher than 94% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • sick.codes https://sick.codes/sick-2021-014 referenced PoC, tagged "exploit" by a source, unverified
  • github.com https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-014.md referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P
OSV 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
bitnami libpython
>=3.8.0, <3.8.12
>=3.9.0, <3.9.5
3.8.12
3.9.5
bitnami python
>=3.8.0, <3.8.12
>=3.9.0, <3.9.5
3.8.12
3.9.5
bitnami python-min
>=3.8.0, <3.8.12
>=3.9.0, <3.9.5
3.8.12
3.9.5

References

Sources

Fencer Intel 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.