CVE-2021-29921

Name: CVE-2021-29921
Creator: NVD / NIST
Published: 2021-05-06T13:15:12.573+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 6.83%

Last modified Jun 17, 2026

CVE-2021-29921 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. 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.. EPSS estimates a 6.83% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

6.83%

93.2th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Python	Python	>= 3.8.0, < 3.8.12
Python	Python	>= 3.9.0, < 3.9.5
Oracle	Communications Cloud Native Core Automated Test Suite	1.8.0
Oracle	Communications Cloud Native Core Binding Support Function	1.11.0
Oracle	Communications Cloud Native Core Network Slice Selection Function	1.8.0
Oracle	Graalvm	20.3.2
Oracle	Graalvm	21.1.0
Oracle	Zfs Storage Appliance Kit	8.8

References

https://bugs.python.org/issue36384Issue Tracking, Patch, Vendor Advisory
https://docs.python.org/3/library/ipaddress.htmlVendor Advisory
https://github.com/python/cpython/blob/63298930fb531ba2bb4f23bc3b915dbf1e17e9e1/Misc/NEWS.d/3.8.0a4.rstThird Party Advisory
https://github.com/python/cpython/pull/12577Patch, Third Party Advisory
https://github.com/python/cpython/pull/25099Patch, Third Party Advisory
https://github.com/sickcodesThird Party Advisory
https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-014.mdExploit, Third Party Advisory
https://python-security.readthedocs.io/vuln/ipaddress-ipv4-leading-zeros.htmlVendor Advisory
https://security.gentoo.org/glsa/202305-02
https://security.netapp.com/advisory/ntap-20210622-0003/Third Party Advisory
https://sick.codes/sick-2021-014Exploit, Third Party Advisory
https://www.oracle.com//security-alerts/cpujul2021.htmlPatch, Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.htmlPatch, Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.htmlPatch, Third Party Advisory
https://www.oracle.com/security-alerts/cpujul2022.html
https://www.oracle.com/security-alerts/cpuoct2021.htmlPatch, Third Party Advisory
https://bugs.python.org/issue36384Issue Tracking, Patch, Vendor Advisory
https://docs.python.org/3/library/ipaddress.htmlVendor Advisory
https://github.com/python/cpython/blob/63298930fb531ba2bb4f23bc3b915dbf1e17e9e1/Misc/NEWS.d/3.8.0a4.rstThird Party Advisory
https://github.com/python/cpython/pull/12577Patch, Third Party Advisory
https://github.com/python/cpython/pull/25099Patch, Third Party Advisory
https://github.com/sickcodesThird Party Advisory
https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-014.mdExploit, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2024/12/msg00000.html
https://python-security.readthedocs.io/vuln/ipaddress-ipv4-leading-zeros.htmlVendor Advisory
https://security.gentoo.org/glsa/202305-02
https://security.netapp.com/advisory/ntap-20210622-0003/Third Party Advisory
https://sick.codes/sick-2021-014Exploit, Third Party Advisory
https://www.oracle.com//security-alerts/cpujul2021.htmlPatch, Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.htmlPatch, Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.htmlPatch, Third Party Advisory
https://www.oracle.com/security-alerts/cpujul2022.html
https://www.oracle.com/security-alerts/cpuoct2021.htmlPatch, Third Party Advisory

Timeline

Published: May 6, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-29921?

How severe is CVE-2021-29921?

CVE-2021-29921 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 6.83% probability of exploitation in the next 30 days.

How do I fix CVE-2021-29921?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-29921?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST