CVE-2021-23017

CRITICALNVD 7.79.4▲
EchelonGraph scoreMEDIUM confidence

Score 9.4 from GitHub Security Advisory (severity: CRITICAL) published 2022-05-24. NVD baseline CVSS 7.7; sources differ by 1.7.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Elevated
9.4EG
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • 824 internet-exposed hosts are running an affected version right now
  • High exploitation likelihood — EPSS 53%
CISA-KEV: Not listedEPSS PROB: 53%CVSS: 7.7Exploit: Elevated riskExposed: 824

A fix is available — apply it.

A security issue in nginx resolver was identified, which might allow an attacker who is able to forge UDP packets from the DNS server to cause 1-byte memory overwrite, resulting in worker process crash or potential other impact.

Live · internet exposure

824 internet-exposed hosts are running an affected version of CVE-2021-23017 right now.

across 66 countries (United States, France, Japan, Germany, China)top: nginx
See the live KEV-Exposure radar →Found passively from public internet-scan data — aggregate, host-redacted.

EchelonGraph is the only CVE feed that fuses live vulnerability intelligence with its own live internet-exposure radar — so you see not just that a CVE is exploited, but how much of the internet is exposed to it right now.

CVSS v3
7.7
EG Score
9.4(medium)
EG Risk
68(Track*)
EG Risk 68/100SSVC: Track*

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
Severity94% × 45%
Exploitation53% × 40%
Automatability30% × 15%
Action: Watch closely — could escalate to Attend.
EPSS PROB
53%
EPSS %ILE
99%
KEV
Not listed

Published

June 1, 2021

Last Modified

November 21, 2024

References (28)

Vendor Advisories for CVE-2021-23017(11)

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

Patch Availability(10)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatnginx:1.20-8050020211221125012.c53685002022-01-31redhat
redhatrhacm2/management-ingress-rhel7:v2.3.3-32021-10-20redhat
redhat3scale-amp2/zync-rhel8:1.14.0-32021-10-14redhat
redhatrhacm2/acm-must-gather-rhel8:v2.1.11-22021-09-23redhat
redhatansible-tower-38/ansible-tower-rhel7:3.8.4-12021-09-08redhat
redhatpython-pulpcore-0:3.7.6-1.el8pc2021-07-29redhat
redhatnginx:1.16-8020020210526102648.4cda2c842021-06-08redhat
redhatnginx:1.18-8040020210526100943.522a0ee42021-06-07redhat
redhatrh-nginx116-nginx-1:1.16.1-6.el72021-06-07redhat
redhatrh-nginx118-nginx-1:1.18.0-3.el72021-06-07redhat

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

(21 across 21 ecosystems)
Alpine:v3.10(1)
PackageVulnerable rangeFixed inDependents
nginx—1.16.1-r3—
Alpine:v3.11(1)
PackageVulnerable rangeFixed inDependents
nginx—1.16.1-r7—
Alpine:v3.12(1)
PackageVulnerable rangeFixed inDependents
nginx—1.18.0-r2—
Alpine:v3.13(1)
PackageVulnerable rangeFixed inDependents
nginx—1.18.0-r14—
Alpine:v3.14(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Alpine:v3.15(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Alpine:v3.16(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Alpine:v3.17(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Alpine:v3.18(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Alpine:v3.19(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Alpine:v3.20(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Alpine:v3.21(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Alpine:v3.22(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Alpine:v3.23(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Alpine:v3.24(1)
PackageVulnerable rangeFixed inDependents
nginx—1.20.1-r0—
Debian:10(1)
PackageVulnerable rangeFixed inDependents
nginx1.14.2-2, 1.14.2-2+deb10u1, 1.14.2-2+deb10u2, 1.14.2-2+deb10u31.14.2-2+deb10u4—
Debian:11(1)
PackageVulnerable rangeFixed inDependents
nginx—1.18.0-6.1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
nginx—1.18.0-6.1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
nginx—1.18.0-6.1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
nginx—1.18.0-6.1—
Debian:9(1)
PackageVulnerable rangeFixed inDependents
nginx1.10.3-1 ... 1.10.3-1+deb9u5 (8 versions)1.10.3-1+deb9u6—

Weakness Classification(1)

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

Additional Vendor Advisories

(2)

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 6× in last 7d / 20× 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 105 total refreshes for this CVE.

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

Publicly available exploits

(2 references)

Working exploit code is in the public domain (1 GitHub PoC) (1 Exploit-DB entry). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • Exploit-DBEDB-50973
    First seen Jul 11, 2022

    Nginx 1.20.0 - Denial of Service (DOS)

    Open source ↗
  • GitHub PoCM507/CVE-2021-23017-PoC
    First seen Jun 30, 2022

    PoC for Nginx 0.6.18 - 1.20.0 Memory Overwrite Vulnerability CVE-2021-23017

    Open source ↗

Frequently asked(5)

What is CVE-2021-23017?
CVE-2021-23017 is a critical vulnerability published on June 1, 2021. A security issue in nginx resolver was identified, which might allow an attacker who is able to forge UDP packets from the DNS server to cause 1-byte memory overwrite, resulting in worker process crash or potential other impact.
When was CVE-2021-23017 disclosed?
CVE-2021-23017 was first published in the National Vulnerability Database on June 1, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-23017 actively exploited?
CVE-2021-23017 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 53% probability of exploitation in the next 30 days, which ranks it in the top 1.1% of all scored CVEs.
What is the CVSS score of CVE-2021-23017?
CVE-2021-23017 has a CVSS v3 base score of 7.7 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.4.
How do I remediate CVE-2021-23017?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-23017, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-23017

Explore →

Is Your Infrastructure Affected by CVE-2021-23017?

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

Start Free Scan →Browse All CVEs