HOMEVULNERABILITIESCVE-2021-29921
CRITICAL

CVE-2021-29921

NVD-CWE-OtherPublished: May 6, 2021· Updated: Jun 17, 2026

9.8
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-29921 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors & Products

Oracle5 product(s)
communications cloud native core automated test suitecommunications cloud native core binding support functioncommunications cloud native core network slice selection functiongraalvmzfs storage appliance kit
Python1 product(s)
python
Source: NVD CPE · 7 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/issue36384
PATCHhttps://github.com/python/cpython/pull/12577
PATCHhttps://github.com/python/cpython/pull/25099
PATCHhttps://www.oracle.com//security-alerts/cpujul2021.html
PATCHhttps://www.oracle.com/security-alerts/cpuapr2022.html
PATCHhttps://www.oracle.com/security-alerts/cpujan2022.html
PATCHhttps://www.oracle.com/security-alerts/cpuoct2021.html
PATCHhttps://bugs.python.org/issue36384
PATCHhttps://github.com/python/cpython/pull/12577
PATCHhttps://github.com/python/cpython/pull/25099
PATCHhttps://www.oracle.com//security-alerts/cpujul2021.html
PATCHhttps://www.oracle.com/security-alerts/cpuapr2022.html
PATCHhttps://www.oracle.com/security-alerts/cpujan2022.html
PATCHhttps://www.oracle.com/security-alerts/cpuoct2021.html
ADVISORYhttps://docs.python.org/3/library/ipaddress.html
ADVISORYhttps://github.com/python/cpython/blob/63298930fb531ba2bb4f23bc3b915dbf1e17e9e1/Misc/NEWS.d/3.8.0a4.rst
ADVISORYhttps://github.com/sickcodes
ADVISORYhttps://github.com/sickcodes/security/blob/master/advisories/SICK-2021-014.md
ADVISORYhttps://python-security.readthedocs.io/vuln/ipaddress-ipv4-leading-zeros.html
ADVISORYhttps://security.netapp.com/advisory/ntap-20210622-0003/
ADVISORYhttps://sick.codes/sick-2021-014
ADVISORYhttps://docs.python.org/3/library/ipaddress.html
ADVISORYhttps://github.com/python/cpython/blob/63298930fb531ba2bb4f23bc3b915dbf1e17e9e1/Misc/NEWS.d/3.8.0a4.rst
ADVISORYhttps://github.com/sickcodes
ADVISORYhttps://github.com/sickcodes/security/blob/master/advisories/SICK-2021-014.md
ADVISORYhttps://python-security.readthedocs.io/vuln/ipaddress-ipv4-leading-zeros.html
ADVISORYhttps://security.netapp.com/advisory/ntap-20210622-0003/
ADVISORYhttps://sick.codes/sick-2021-014

All References (33)

→
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

Quick Facts

CVE IDCVE-2021-29921
CVSS Score9.8 / 10
SeverityCRITICAL
WeaknessNVD-CWE-Other
CISA KEVNo
Affected2 vendor(s)
PublishedMay 6, 2021

Related CVEs (NVD-CWE-Other)

CVE-2000-0506
10.0
CVE-2003-1140
10.0
CVE-2000-1220
10.0
CVE-2002-0525
10.0
CVE-2004-0084
10.0
CVE-2007-1866
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-29921 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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