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.
  • 538 internet-facing services (distinct ip:port) on record running an affected version — derived from Shodan data (© Shodan); a patched service can stay counted while its port stays open
  • High exploitation likelihood — EPSS 53%
CISA-KEV: Not listedEPSS PROB: 53%CVSS: 7.7Exploit: Elevated riskExposed services: 538

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.

Internet exposure · derived from Shodan data

538 internet-facing services (distinct ip:port) on record running a version that maps to CVE-2021-23017, in our KEV-Exposure radar’s Shodan-derived sample.

across 58 countries (United States, Japan, China, Germany, United Kingdom)top: nginx
See the KEV-Exposure radar →Derived from Shodan data. Shodan data is owned by Shodan, which holds its copyright (© Shodan). EchelonGraph claims no ownership of it or copyright in it. Aggregate, host-redacted.

How it counts: every 12 hours, when Shodan query credits allow, the radar runs one Shodan query per tracked product, reads up to 100 ip:port services per query, and keeps a service when its banner version matches a CISA-KEV or high-EPSS CVE; a service is dropped when neither a search nor a Shodan InternetDB port re-check has refreshed it for 21 days. A re-check that finds the port still listed by Shodan InternetDB refreshes the service without re-reading the banner, so a patched service can stay counted while its port stays open. A count is a banner-version inference over a sample, not an exploit test and not an internet-wide census, and the unit is a service, not a machine: a machine answering on two ports counts twice.

CVSS v3
7.7
EG Score
9.4CRITICALmedium confidence
EG Risk
68
EG Risk 68/100CISA 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
Severity94% × 45%
Exploitation53% × 40%
Automatability30% × 15%
CISA SSVC: Track at low, Track* at medium and Attend at high mission impact.
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
53%
EPSS %ILE
98th
KEV
Not listed

CISA SSVCTrack at low, Track* at medium and Attend at high mission impact.

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

Exploitation public PoC (EG-KEV: elevated) · 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

June 1, 2021

Last Modified

November 21, 2024

References (28)

Vendor Advisories for CVE-2021-23017(12)

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 / EcosystemFix (by version range) / 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 rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.16.1-r3: fixed in 1.16.1-r3
—
Alpine:v3.11(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.16.1-r7: fixed in 1.16.1-r7
—
Alpine:v3.12(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.18.0-r2: fixed in 1.18.0-r2
—
Alpine:v3.13(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.18.0-r14: fixed in 1.18.0-r14
—
Alpine:v3.14(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Alpine:v3.15(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Alpine:v3.16(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Alpine:v3.17(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Alpine:v3.18(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Alpine:v3.19(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Alpine:v3.20(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Alpine:v3.21(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Alpine:v3.22(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Alpine:v3.23(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Alpine:v3.24(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • 0.6.18 up to 1.20.1-r0: fixed in 1.20.1-r0
—
Debian:10(1)
PackageVulnerable rangeFix by version rangeDependents
nginx1.14.2-2, 1.14.2-2+deb10u1, 1.14.2-2+deb10u2, 1.14.2-2+deb10u3
  • every version up to 1.14.2-2+deb10u4: fixed in 1.14.2-2+deb10u4
—
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • every version up to 1.18.0-6.1: fixed in 1.18.0-6.1
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • every version up to 1.18.0-6.1: fixed in 1.18.0-6.1
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • every version up to 1.18.0-6.1: fixed in 1.18.0-6.1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
nginx—
  • every version up to 1.18.0-6.1: fixed in 1.18.0-6.1
—
Debian:9(1)
PackageVulnerable rangeFix by version rangeDependents
nginx1.10.3-1 ... 1.10.3-1+deb9u5 (8 versions)
  • every version up to 1.10.3-1+deb9u6: fixed in 1.10.3-1+deb9u6
—

Weakness Classification(1)

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

Additional Vendor Advisories

(1)

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 7× in last 7d / 28× 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 145 total refreshes for this CVE.

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

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 ↗

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

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 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 (98th percentile of EPSS-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 (CRITICAL).
How do I remediate CVE-2021-23017?
A fix for CVE-2021-23017 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2021-23017 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-2021-23017

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