CVE-2009-0021

MEDIUMCVSS v2 · 5.05.0—
EchelonGraph scoreLOW confidence

This CVE was only ever scored under CVSS v2.0. NVD CVSS v2.0 base 5.0 — v2 rates that MEDIUM (v2 bands: LOW 0.0–3.9 / MEDIUM 4.0–6.9 / HIGH 7.0–10.0; v2 has no CRITICAL band). Vector AV:N/AC:L/Au:N/C:P/I:N/A:N. CVSS v2 is an older, coarser metric than v3.1/v4.0 (no Scope, no User Interaction, no Attack Requirements), so it is not directly comparable to a v3 or v4 score. NVD has never re-scored this record under v3. EPSS predicts 3.2% exploitation probability in the next 30 days, which is reflected in EG Risk but does not lift the v2 base. Confidence: LOW.

Triggered by: NVD CVSS v2.0 (legacy fallback)
Sources: epss, nvd_v2
5.0EG
EchelonGraph verdictMonitorRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 3.2%CVSS v2: 5.0Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

NTP 4.2.4 before 4.2.4p5 and 4.2.5 before 4.2.5p150 does not properly check the return value from the OpenSSL EVP_VerifyFinal function, which allows remote attackers to bypass validation of the certificate chain via a malformed SSL/TLS signature for DSA and ECDSA keys, a similar vulnerability to CVE-2008-5077.

CVSS v2.0 (legacy)
5.0MEDIUMNVD never assigned a CVSS v3 rating to this CVE
EG Score
5.0MEDIUMlow confidence
EG Risk
28
EG Risk 28/100

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 (value × EchelonGraph’s weight)
Severity50% × 45%
The EG Score, 5.0 of 10.
Exploitation3% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability30% × 15%
EchelonGraph's default: CISA has not published Automatable for this CVE.
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track or Track* or Attend at high (mission-essential systems).
Exploitation none (no KEV listing, exploit record or EPSS ≥ 50%) · Automatable unknown (not published for this CVE) · Technical impact unknown (not published for this CVE). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
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
3.2%
EPSS %ILE
87th
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track or 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 unknown (not published for this CVE). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

Published

January 7, 2009

Last Modified

April 23, 2026

References (19)

15 of 19 shown · show the other 4

Patch Availability(2)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
ubuntuntp (1:4.2.4p4+dfsg-6ubuntu2.2) @ intrepid2026-05-30ubuntu
redhatntp-0:4.2.2p1-9.el5_3.12009-01-29redhat

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

(2 across 2 ecosystems)
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
ntp—
  • every version up to 1:4.2.4p4+dfsg-8: fixed in 1:4.2.4p4+dfsg-8
—
Debian:4.0(1)
PackageVulnerable rangeFix by version rangeDependents
ntp1:4.2.2.p4+dfsg-2
  • every version up to 1:4.2.2.p4+dfsg-2etch1: fixed in 1:4.2.2.p4+dfsg-2etch1
—

Weakness Classification(1)

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

All Vendor Advisories

(2)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 8× in last 7d / 19× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 83 of 124 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 17 repeat rows among the latest 100 are merged into the row they repeat. The 41 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-11 13:38 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  2. 2026-10-10 19:54 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  3. 2026-10-09 20:00 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  4. 2026-10-08 16:33 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  5. 2026-10-07 23:37 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  6. 2026-10-06 15:09 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  7. 2026-10-05 17:37 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  8. 2026-10-04 23:15 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  9. 2026-10-03 21:28 UTCOSV refresh
  10. 2026-09-30 14:58 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  11. 2026-09-29 07:56 UTCEG score recompute
  12. 2026-09-27 13:39 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  13. 2026-09-26 15:52 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  14. 2026-09-24 13:57 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  15. 2026-09-17 19:20 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  16. 2026-09-15 03:04 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  17. 2026-09-14 11:44 UTCOSV refresh
  18. 2026-09-13 16:40 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  19. 2026-09-12 14:54 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  20. 2026-09-10 09:24 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  21. 2026-09-06 13:41 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  22. 2026-09-05 15:22 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  23. 2026-09-04 13:55 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  24. 2026-08-28 21:34 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  25. 2026-08-27 14:19 UTCEPSS rescoreEPSS 3.2% · 87th percentile
Show 58 more
  1. 2026-08-26 13:02 UTCOSV refresh
  2. 2026-08-25 13:43 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  3. 2026-08-19 16:58 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  4. 2026-08-15 01:24 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  5. 2026-08-10 01:40 UTCOSV refresh
  6. 2026-08-09 13:41 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  7. 2026-08-08 16:31 UTCEPSS rescoreEPSS 3.2% · 87th percentile
  8. 2026-08-06 13:41 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  9. 2026-08-03 10:28 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  10. 2026-07-30 16:22 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  11. 2026-07-30 01:26 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  12. 2026-07-26 13:37 UTCEG score recompute▲ 5.00
  13. 2026-07-25 14:12 UTCEPSS rescoreEPSS 3.1% · 86th percentile
  14. 2026-07-25 02:41 UTCOSV refresh
  15. 2026-07-24 14:12 UTCEPSS rescoreEPSS 3.1% · 86th percentile
  16. 2026-07-23 14:14 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  17. 2026-07-23 00:58 UTCEG score recompute
  18. 2026-07-23 00:36 UTCEG score recompute
  19. 2026-07-23 00:03 UTCEG score recompute
  20. 2026-07-22 21:42 UTCEG score recompute
  21. 2026-07-22 14:03 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  22. 2026-07-21 15:20 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  23. 2026-07-20 17:03 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  24. 2026-07-18 09:59 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  25. 2026-07-16 16:58 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  26. 2026-07-15 16:54 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  27. 2026-07-15 01:55 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  28. 2026-07-13 22:25 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  29. 2026-07-13 06:07 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  30. 2026-07-11 08:22 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  31. 2026-07-09 19:04 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  32. 2026-07-08 15:10 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  33. 2026-07-07 21:27 UTCOSV refresh
  34. 2026-07-06 16:23 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  35. 2026-07-06 02:19 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  36. 2026-07-05 02:26 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  37. 2026-07-04 06:27 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  38. 2026-07-01 15:02 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  39. 2026-06-30 23:19 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  40. 2026-06-28 04:52 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  41. 2026-06-27 03:05 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  42. 2026-06-25 13:46 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  43. 2026-06-24 14:02 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  44. 2026-06-23 21:29 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  45. 2026-06-22 14:22 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  46. 2026-06-21 14:53 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  47. 2026-06-21 01:56 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  48. 2026-06-19 19:22 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  49. 2026-06-19 09:25 UTCOSV refresh
  50. 2026-06-18 17:49 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  51. 2026-06-17 17:49 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  52. 2026-06-16 17:49 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  53. 2026-06-15 17:44 UTCEPSS rescoreEPSS 3.2% · 86th percentile
  54. 2026-06-14 23:14 UTCEPSS rescoreEPSS 2.2% · 84th percentile
  55. 2026-06-13 22:57 UTCEPSS rescoreEPSS 2.2% · 84th percentile
  56. 2026-06-12 23:08 UTCEPSS rescoreEPSS 2.2% · 84th percentile
  57. 2026-06-10 22:14 UTCEPSS rescoreEPSS 2.2% · 84th percentile
  58. 2026-06-10 13:17 UTCEPSS rescoreEPSS 2.2% · 84th percentile

Related CVEs(same product + same CWE)

Frequently asked(4)

What is CVE-2009-0021?
CVE-2009-0021 is a medium vulnerability published on January 7, 2009. NTP 4.2.4 before 4.2.4p5 and 4.2.5 before 4.2.5p150 does not properly check the return value from the OpenSSL EVP_VerifyFinal function, which allows remote attackers to bypass validation of the certificate chain via a malformed SSL/TLS signature for DSA and ECDSA keys, a similar vulnerability to…
When was the CVE record for CVE-2009-0021 published?
The CVE record for CVE-2009-0021 was published on January 7, 2009. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of April 23, 2026; the record at its source may have been updated since.
Is CVE-2009-0021 actively exploited?
CVE-2009-0021 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 3.2% probability of exploitation in the next 30 days (87th percentile of EPSS-scored CVEs).
How do I remediate CVE-2009-0021?
A fix for CVE-2009-0021 is available: update to the fixed version the vendor names in its advisory.

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