CVE-2021-29921

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2022-05-24. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 6.9%CVSS: 9.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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.

CVSS v3
9.8
EG Score
9.8CRITICALmedium confidence
EG Risk
51
EG Risk 51/100CISA SSVC

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation7% × 40%
Automatability30% × 15%
CISA SSVC: Track at low or medium mission impact; Track* or Attend at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
6.9%
EPSS %ILE
93rd
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track* or Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (no KEV listing, exploit record or EPSS ≥ 50%) · Automatable unknown (not published for this CVE) · Technical impact total (CVSS ≥ 9.0). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

May 6, 2021

Last Modified

November 3, 2025

Advisory Details (10)

Auto-updated Oct 1, 2026
🔬 Proof of concept available. Patch available. Sources: github_pr, github.
generic

NetApp Product Security

https://security.netapp.com/advisory/ntap-20210622-0003/
generic

Python, PyPy3: Multiple Vulnerabilities (GLSA 202305-02) — Gentoo security

https://security.gentoo.org/glsa/202305-02
generic

ipaddress leading zeros in IPv4 address — Python Security 0.0 documentation

https://python-security.readthedocs.io/vuln/ipaddress-ipv4-leading-zeros.html
github🟡 PoC Available

security/advisories/SICK-2021-014.md at master · sickcodes/security · GitHub

https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-014.md
generic

sickcodes (sickcodes) · GitHub

https://github.com/sickcodes
github_pr

bpo-36384: Leading zeros in IPv4 addresses are no longer tolerated

Fix merged in python/cpython PR #25099 on 2021-05-02 — awaiting tagged release

https://github.com/python/cpython/pull/25099
github_pr

bpo-36384: Remove check for leading zeroes in IPv4 addresses

Fix merged in python/cpython PR #12577 on 2019-03-30 — awaiting tagged release

https://github.com/python/cpython/pull/12577
generic

cpython/Misc/NEWS.d/3.8.0a4.rst at 63298930fb531ba2bb4f23bc3b915dbf1e17e9e1 · python/cpython · GitHub

https://github.com/python/cpython/blob/63298930fb531ba2bb4f23bc3b915dbf1e17e9e1/Misc/NEWS.d/3.8.0a4.rst
generic

ipaddress — IPv4/IPv6 manipulation library — Python 3.14.8 documentation

https://docs.python.org/3/library/ipaddress.html
generic

Issue 36384: [security] CVE-2021-29921: ipaddress Should not reject IPv4 addresses with leading zeroes as ambiguously octal - Python tracker

https://bugs.python.org/issue36384

Vendor Advisories for CVE-2021-29921(3)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(6)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
ubuntupython3.8-venv (3.8.0-3ubuntu1~18.04.2+esm2) @ bionic2026-05-26ubuntu
ubuntupython3.8-doc (3.8.10-0ubuntu1~20.04.1) @ focal2026-05-26ubuntu
ubuntupython3.8-doc (3.8.6-1ubuntu0.3) @ groovy2026-05-26ubuntu
redhatpython39-devel:3.9-8050020210811100211.d428a79b2021-11-09redhat
redhatpython38-devel:3.8-8050020210811101222.e3d35cca2021-11-09redhat
redhatrh-python38-python-urllib3-0:1.25.7-7.el72021-08-24redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(14 across 14 ecosystems)
Alpine:v3.15(1)
PackageVulnerable rangeFix by version rangeDependents
python3—
  • every version up to 3.9.5-r0: fixed in 3.9.5-r0
—
Alpine:v3.16(1)
PackageVulnerable rangeFix by version rangeDependents
python3—
  • every version up to 3.9.5-r0: fixed in 3.9.5-r0
—
Alpine:v3.17(1)
PackageVulnerable rangeFix by version rangeDependents
python3—
  • every version up to 3.9.5-r0: fixed in 3.9.5-r0
—
Alpine:v3.18(1)
PackageVulnerable rangeFix by version rangeDependents
python3—
  • every version up to 3.9.5-r0: fixed in 3.9.5-r0
—
Alpine:v3.19(1)
PackageVulnerable rangeFix by version rangeDependents
python3—
  • every version up to 3.9.5-r0: fixed in 3.9.5-r0
—
Alpine:v3.20(1)
PackageVulnerable rangeFix by version rangeDependents
python3—
  • every version up to 3.9.5-r0: fixed in 3.9.5-r0
—
Alpine:v3.21(1)
PackageVulnerable rangeFix by version rangeDependents
python3—
  • every version up to 3.9.5-r0: fixed in 3.9.5-r0
—
Alpine:v3.22(1)
PackageVulnerable rangeFix by version rangeDependents
python3—
  • every version up to 3.9.5-r0: fixed in 3.9.5-r0
—
Alpine:v3.23(1)
PackageVulnerable rangeFix by version rangeDependents
python3—
  • every version up to 3.9.5-r0: fixed in 3.9.5-r0
—
Alpine:v3.24(1)
PackageVulnerable rangeFix by version rangeDependents
python3—
  • every version up to 3.9.5-r0: fixed in 3.9.5-r0
—
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
python3.93.9.2-1, 3.9.2-1+deb11u1
  • every version up to 3.9.2-1+deb11u2: fixed in 3.9.2-1+deb11u2
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
pypy3—
  • every version up to 7.3.8+dfsg-1: fixed in 7.3.8+dfsg-1
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
pypy3—
  • every version up to 7.3.8+dfsg-1: fixed in 7.3.8+dfsg-1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
pypy3—
  • every version up to 7.3.8+dfsg-1: fixed in 7.3.8+dfsg-1
—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Additional Vendor Advisories

(3)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 9× in last 7d / 32× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 176 total refreshes for this CVE.

  1. 2026-10-05 17:40 UTCEPSS rescore
  2. 2026-10-04 23:19 UTCEPSS rescore
  3. 2026-10-03 14:22 UTCEPSS rescore
  4. 2026-10-03 14:22 UTCEPSS rescore
  5. 2026-10-02 16:22 UTCEPSS rescore
  6. 2026-10-01 19:46 UTCEPSS rescore
  7. 2026-09-30 15:34 UTCEG score recompute
  8. 2026-09-30 15:00 UTCEPSS rescore
  9. 2026-09-29 15:15 UTCEPSS rescore
  10. 2026-09-28 13:47 UTCEPSS rescore
  11. 2026-09-27 13:41 UTCEPSS rescore
  12. 2026-09-26 15:54 UTCEPSS rescore
  13. 2026-09-26 15:54 UTCEPSS rescore
  14. 2026-09-26 03:12 UTCOSV refresh
  15. 2026-09-26 00:21 UTCEPSS rescore
  16. 2026-09-24 14:00 UTCEPSS rescore
  17. 2026-09-23 13:44 UTCEPSS rescore
  18. 2026-09-21 20:28 UTCEPSS rescore
  19. 2026-09-19 15:37 UTCEPSS rescore
  20. 2026-09-18 19:23 UTCEPSS rescore
  21. 2026-09-17 19:23 UTCEPSS rescore
  22. 2026-09-17 19:23 UTCEPSS rescore
  23. 2026-09-16 14:05 UTCEPSS rescore
  24. 2026-09-15 03:06 UTCEPSS rescore
  25. 2026-09-15 03:06 UTCEPSS rescore
Show 75 more
  1. 2026-09-12 14:57 UTCEPSS rescore
  2. 2026-09-11 14:49 UTCEPSS rescore
  3. 2026-09-11 09:33 UTCEPSS rescore
  4. 2026-09-08 21:56 UTCEPSS rescore
  5. 2026-09-07 15:58 UTCEPSS rescore
  6. 2026-09-06 17:43 UTCOSV refresh
  7. 2026-09-06 13:44 UTCEPSS rescore
  8. 2026-09-05 15:25 UTCEPSS rescore
  9. 2026-09-04 13:57 UTCEPSS rescore
  10. 2026-09-04 05:03 UTCEPSS rescore
  11. 2026-09-04 05:03 UTCEPSS rescore
  12. 2026-09-02 14:08 UTCEPSS rescore
  13. 2026-09-01 13:50 UTCEPSS rescore
  14. 2026-09-01 03:32 UTCEPSS rescore
  15. 2026-08-30 19:14 UTCEPSS rescore
  16. 2026-08-30 01:19 UTCEPSS rescore
  17. 2026-08-28 21:37 UTCEPSS rescore
  18. 2026-08-27 14:22 UTCEPSS rescore
  19. 2026-08-26 14:42 UTCEPSS rescore
  20. 2026-08-25 13:45 UTCEPSS rescore
  21. 2026-08-24 14:12 UTCEPSS rescore
  22. 2026-08-23 00:16 UTCEPSS rescore
  23. 2026-08-21 23:46 UTCEPSS rescore
  24. 2026-08-20 22:52 UTCEPSS rescore
  25. 2026-08-20 04:04 UTCOSV refresh
  26. 2026-08-19 17:01 UTCEPSS rescore
  27. 2026-08-18 13:45 UTCEPSS rescore
  28. 2026-08-16 14:53 UTCEPSS rescore
  29. 2026-08-16 02:11 UTCEPSS rescore
  30. 2026-08-16 02:11 UTCEPSS rescore
  31. 2026-08-15 01:27 UTCEPSS rescore
  32. 2026-08-13 21:57 UTCEPSS rescore
  33. 2026-08-12 13:47 UTCEPSS rescore
  34. 2026-08-11 13:38 UTCEPSS rescore
  35. 2026-08-08 16:33 UTCEPSS rescore
  36. 2026-08-07 16:23 UTCEPSS rescore
  37. 2026-08-06 13:43 UTCEPSS rescore
  38. 2026-08-05 19:14 UTCEPSS rescore
  39. 2026-08-04 23:10 UTCOSV refresh
  40. 2026-08-04 15:06 UTCEPSS rescore
  41. 2026-08-04 10:34 UTCEPSS rescore
  42. 2026-08-03 10:33 UTCEPSS rescore
  43. 2026-08-02 02:24 UTCEPSS rescore
  44. 2026-08-01 04:13 UTCEPSS rescore
  45. 2026-07-30 16:25 UTCEPSS rescore
  46. 2026-07-30 16:25 UTCEPSS rescore
  47. 2026-07-30 01:28 UTCEPSS rescore
  48. 2026-07-30 01:27 UTCEPSS rescore
  49. 2026-07-28 15:33 UTCEPSS rescore
  50. 2026-07-25 14:15 UTCEPSS rescore
  51. 2026-07-24 14:15 UTCEPSS rescore
  52. 2026-07-23 14:16 UTCEPSS rescore
  53. 2026-07-23 02:00 UTCEG score recompute
  54. 2026-07-22 22:47 UTCEG score recompute
  55. 2026-07-22 14:06 UTCEPSS rescore
  56. 2026-07-22 14:06 UTCEPSS rescore
  57. 2026-07-21 15:22 UTCEPSS rescore
  58. 2026-07-21 15:22 UTCEPSS rescore
  59. 2026-07-20 17:05 UTCEPSS rescore
  60. 2026-07-19 14:28 UTCEPSS rescore
  61. 2026-07-19 02:27 UTCEPSS rescore
  62. 2026-07-19 02:27 UTCEPSS rescore
  63. 2026-07-18 20:59 UTCOSV refresh
  64. 2026-07-18 10:02 UTCEPSS rescore
  65. 2026-07-18 10:02 UTCEPSS rescore
  66. 2026-07-16 17:00 UTCEPSS rescore
  67. 2026-07-15 16:55 UTCEPSS rescore
  68. 2026-07-15 16:55 UTCEPSS rescore
  69. 2026-07-15 01:58 UTCEPSS rescore
  70. 2026-07-13 22:27 UTCEPSS rescore
  71. 2026-07-13 22:27 UTCEPSS rescore
  72. 2026-07-13 06:10 UTCEPSS rescore
  73. 2026-07-12 05:44 UTCEPSS rescore
  74. 2026-07-12 05:44 UTCEPSS rescore
  75. 2026-07-11 08:25 UTCEPSS rescore

Related CVEs(same product + same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-29921?
CVE-2021-29921 is a critical vulnerability published on May 6, 2021. 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.
When was CVE-2021-29921 disclosed?
CVE-2021-29921 was first published on May 6, 2021, with the most recent update on November 3, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-29921 actively exploited?
CVE-2021-29921 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 6.9% probability of exploitation in the next 30 days (93rd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-29921?
CVE-2021-29921 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-29921?
A fix for CVE-2021-29921 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2021-29921 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-29921

Explore →

Is Your Infrastructure Affected by CVE-2021-29921?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Book a Demo →Browse All CVEs