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CRITICAL

CVE-2021-29921

CVSS v3

9.8

CRITICAL

EPSS Score

6.9 %

exploit probability, as of 2026-10-18

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • pythonBitnamifrom 3.8.0 · fixed in 3.8.12and 2 other packages
  • python38-asn1cryptoAlmaLinux:8all versions · fixed in 1.2.0-3.module_el8.6.0+2778+cd494b30
  • python38-atomicwritesAlmaLinux:8all versions · fixed in 1.3.0-8.module_el8.6.0+2778+cd494b30
  • python38-attrsAlmaLinux:8all versions · fixed in 19.3.0-3.module_el8.6.0+2778+cd494b30
  • python38-babelAlmaLinux:8all versions · fixed in 2.7.0-11.module_el8.6.0+2778+cd494b30
  • python38-cffiAlmaLinux:8all versions · fixed in 1.13.2-3.module_el8.6.0+2778+cd494b30
  • python38-chardetAlmaLinux:8all versions · fixed in 3.0.4-19.module_el8.6.0+2778+cd494b30
  • python38-cryptographyAlmaLinux:8all versions · fixed in 2.8-3.module_el8.6.0+2778+cd494b30

57 more package ranges on OSV.dev

Vendor advisories

  • CVE-2021-29921 Red Hat Product Security594 products fixed

    python-ipaddress: Improper input validation of octal strings

  • RHSA-2021:4160 Red Hat Product Security229 products fixed

    Red Hat Security Advisory: python39:3.9 and python39-devel:3.9 security update

  • RHSA-2021:4162 Red Hat Product Security239 products fixed

    Red Hat Security Advisory: python38:3.8 and python38-devel:3.8 security update

  • RHSA-2021:3254 Red Hat Product Security126 products fixed

    Red Hat Security Advisory: rh-python38 security, bug fix, and enhancement update

Full record on NVD

Description

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.

Technical details

Published
2021-05-06

Frequently asked questions

What is CVE-2021-29921?

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.

Is CVE-2021-29921 actively exploited?

Active exploitation of CVE-2021-29921 has not been confirmed. Its EPSS score was 6.9% on 2026-10-18, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-29921?

CVE-2021-29921 has a CVSS v3 base score of 9.8 (CRITICAL severity).

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