CVE-2021-29921: In Python before 3,9,5, the ipaddress library mishandles leading zero characters in the octets of an IP address string.
Noroxi assessment
Priority: Plan (action score 41/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 6.7% (FIRST EPSS); higher than 94% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
- According to CISA the attack is automatable: targets can be found by mass scanning.
- Fixed version: python38-asn1crypto (AlmaLinux:8) 1.2.0-3.module_el8.6.0+2778+cd494b30; python38-atomicwrites (AlmaLinux:8) 1.3.0-8.module_el8.6.0+2778+cd494b30; python38-attrs (AlmaLinux:8) 19.3.0-3.module_el8.6.0+2778+cd494b30.
Add it to your regular patch cycle. Upgrade to python38-asn1crypto (AlmaLinux:8) 1.2.0-3.module_el8.6.0+2778+cd494b30; python38-atomicwrites (AlmaLinux:8) 1.3.0-8.module_el8.6.0+2778+cd494b30; python38-attrs (AlmaLinux:8) 19.3.0-3.module_el8.6.0+2778+cd494b30 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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.
- Published
- May 6, 2021
- Updated
- Oct 8, 2026
- EPSS
- 6.7% · 94th percentile
- CWE
- —
Report tools
Action score
41
Add it to your regular patch cycle.
- CVSS
- 39 / 40 · 9.8 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 2 / 30 · 6.7%
CISA SSVC decision
- Exploitation
- none
- Automatable
- yes
- Technical impact
- total
Vulnrichment: CISA's decision-tree inputs.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
Is your version affected? Check itNoroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| python | python | cpe:2.3:a:python:python |
| oracle | communications cloud native core automated test suite | cpe:2.3:a:oracle:communications_cloud_native_core_automated_test_suite |
| oracle | communications cloud native core binding support function | cpe:2.3:a:oracle:communications_cloud_native_core_binding_support_function |
| oracle | communications cloud native core network slice selection function | cpe:2.3:a:oracle:communications_cloud_native_core_network_slice_selection_function |
| oracle | graalvm | cpe:2.3:a:oracle:graalvm |
| oracle | zfs storage appliance kit | cpe:2.3:a:oracle:zfs_storage_appliance_kit |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- oracle communications cloud native core automated test suite1.8.0
- oracle communications cloud native core binding support function1.11.0
- oracle communications cloud native core network slice selection function1.8.0
- oracle graalvm20.3.2
- oracle graalvm21.1.0
- oracle zfs storage appliance kit8.8
- python python3.9.0 and later · before 3.9.5
- python python3.8.0 and later · before 3.8.12
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| AlmaLinux:8 | python38-asn1crypto | before 1.2.0-3.module_el8.6.0+2778+cd494b30 | 1.2.0-3.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-atomicwrites | before 1.3.0-8.module_el8.6.0+2778+cd494b30 | 1.3.0-8.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-attrs | before 19.3.0-3.module_el8.6.0+2778+cd494b30 | 19.3.0-3.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-babel | before 2.7.0-11.module_el8.6.0+2778+cd494b30 | 2.7.0-11.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-cffi | before 1.13.2-3.module_el8.6.0+2778+cd494b30 | 1.13.2-3.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-chardet | before 3.0.4-19.module_el8.6.0+2778+cd494b30 | 3.0.4-19.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-cryptography | before 2.8-3.module_el8.6.0+2778+cd494b30 | 2.8-3.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-Cython | before 0.29.14-4.module_el8.6.0+2778+cd494b30 | 0.29.14-4.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-idna | before 2.8-6.module_el8.6.0+2778+cd494b30 | 2.8-6.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-jinja2 | before 2.10.3-5.module_el8.6.0+2778+cd494b30 | 2.10.3-5.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-markupsafe | before 1.1.1-6.module_el8.6.0+2778+cd494b30 | 1.1.1-6.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-mod_wsgi | before 4.6.8-3.module_el8.6.0+2778+cd494b30 | 4.6.8-3.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-more-itertools | before 7.2.0-5.module_el8.6.0+2778+cd494b30 | 7.2.0-5.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-numpy | before 1.17.3-6.module_el8.6.0+2778+cd494b30 | 1.17.3-6.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-numpy-doc | before 1.17.3-6.module_el8.6.0+2778+cd494b30 | 1.17.3-6.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-numpy-f2py | before 1.17.3-6.module_el8.6.0+2778+cd494b30 | 1.17.3-6.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-packaging | before 19.2-3.module_el8.6.0+2778+cd494b30 | 19.2-3.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-pluggy | before 0.13.0-3.module_el8.6.0+2778+cd494b30 | 0.13.0-3.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-ply | before 3.11-10.module_el8.6.0+2778+cd494b30 | 3.11-10.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-psutil | before 5.6.4-4.module_el8.6.0+2778+cd494b30 | 5.6.4-4.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-psycopg2 | before 2.8.4-4.module_el8.6.0+2778+cd494b30 | 2.8.4-4.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-psycopg2-doc | before 2.8.4-4.module_el8.6.0+2778+cd494b30 | 2.8.4-4.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-psycopg2-tests | before 2.8.4-4.module_el8.6.0+2778+cd494b30 | 2.8.4-4.module_el8.6.0+2778+cd494b30 |
| AlmaLinux:8 | python38-py | before 1.8.0-8.module_el8.6.0+2778+cd494b30 | 1.8.0-8.module_el8.6.0+2778+cd494b30 |
+96
Same product
python: all recordsOther highest-scoring records for the same primary product.
- CVE-2016-5636Integer overflow in the get_data function in zipimport.c in CPython (aka Python) before 2.7.12, 3.x before 3.4.5, and 3.5.x before 3.5.2…47Plan
- CVE-2007-4559Directory traversal vulnerability in the (1) extract and (2) extractall functions in the tarfile module in Python allows user-assisted…47Plan
- CVE-2021-3177Python 3.x through 3.9.1 has a buffer overflow in PyCArg_repr in _ctypes/callproc.c, which may lead to remote code execution in certain…46Plan
Published before and after this one in the same product
- ← EarlierCVE-2021-23336Feb 15, 2021 · The package python/cpython from 0 and before 3.6.13, from 3.7.0 and before 3.7.10, from 3.8.0 and before 3.8.8, from 3.9.0 and before 3.9.2…35Monitor
- ← EarlierCVE-2021-32052May 6, 2021 · In Django 2.2 before 2.2.22, 3.1 before 3.1.10, and 3.2 before 3.2.2 (with Python 3.9.5+), URLValidator does not prohibit newlines and tabs…25Monitor
- Later →CVE-2021-3426May 20, 2021 · There's a flaw in Python 3's pydoc.23Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| almalinux:python39-attrs | 20.3.0-2.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-cffi | 1.14.3-2.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-chardet | 3.0.4-19.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-cryptography | 3.3.1-2.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-Cython | 0.29.21-5.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-idna | 2.10-3.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-iniconfig | 1.1.1-2.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-mod_wsgi | 4.7.1-4.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-more-itertools | 8.5.0-2.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-numpy | 1.19.4-3.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-numpy-doc | 1.19.4-3.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:python39-PyMySQL | 0.10.1-2.module_el8.6.0+2780+a40f65e1 · AlmaLinux:8 | Package registry (OSV) |
| alpine:python3 | 3.9.5-r0 · Alpine:v3.15 | Package registry (OSV) |
| debian:pypy3 | 7.3.8+dfsg-1 · Debian:12 | Package registry (OSV) |
| debian:python3.9 | 3.9.2-1+deb11u2 · Debian:11 | Package registry (OSV) |
| opensuse:python39 | 3.9.7-2.1 · openSUSE:Tumbleweed | Package registry (OSV) |
| red hat:rh-python38-babel | 0:2.7.0-12.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python | 0:3.8.11-2.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python-babel | 0:2.7.0-12.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python-cryptography | 0:2.8-5.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python-cryptography-debuginfo | 0:2.8-5.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python-debug | 0:3.8.11-2.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python-debuginfo | 0:3.8.11-2.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python-devel | 0:3.8.11-2.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python-idle | 0:3.8.11-2.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python-jinja2 | 0:2.10.3-6.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python-libs | 0:3.8.11-2.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-python38-python-lxml | 0:4.4.1-7.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| rocky linux:Cython | 0:0.29.21-5.module+el8.4.0+574+843c4898 · Rocky Linux:8 | Package registry (OSV) |
| rocky linux:mod_wsgi | 0:4.7.1-4.module+el8.4.0+574+843c4898 · Rocky Linux:8 | Package registry (OSV) |
+12
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Not on record for this CVE: EPSS history · researcher credit · variant or chain candidate · public bounty program.
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- high · data can be read
- Integrity
- high · data or configuration can be modified
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
Weakness class (CWE)
—
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log (2)
- SSVC exploitation— → none
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (14 more)Show less
- docs.python.org/3/library/ipaddress.html
- github.com/python/cpython/blob/63298930fb531ba2bb4f23bc3b915dbf1e17e9e1/Misc/NEWS.d/3.8.0a4.rst
- github.com/python/cpython/pull/12577
- github.com/python/cpython/pull/25099
- github.com/sickcodes
- python-security.readthedocs.io/vuln/ipaddress-ipv4-leading-zeros.html
- security.gentoo.org/glsa/202305-02
- security.netapp.com/advisory/ntap-20210622-0003/
- www.oracle.com//security-alerts/cpujul2021.html
- www.oracle.com/security-alerts/cpuapr2022.html
- www.oracle.com/security-alerts/cpujan2022.html
- www.oracle.com/security-alerts/cpujul2022.html
- www.oracle.com/security-alerts/cpuoct2021.html
- lists.debian.org/debian-lts-announce/2024/12/msg00000.html
Vendor advisories and official records. Exploit/PoC links are deliberately left out.