CVE-2026-42923

MEDIUMNVD 5.35.3—
EchelonGraph scoreMEDIUM confidence

Score 5.3 from GitHub Security Advisory published 2026-05-20. NVD baseline CVSS 5.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
5.3
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 5.3Exploit: NoneExposed: 0

A fix is available — apply it.

NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound. Unbound will keep performing the allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in 1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable code path with the existing limit for NSEC3 hash calculations.

CVSS v3
5.3
EG Score
5.3(medium)
EG Risk
—
EPSS
26.3%
KEV
Not listed

Published

May 20, 2026

Last Modified

May 20, 2026

Advisory Details (1)

Auto-updated May 20, 2026
No patch confirmed yet.
generic
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42923.txt

Vendor Advisories for CVE-2026-42923(3)

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

Patch Availability(2)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuunbound-host (1.19.2-1ubuntu3.8) @ noble2026-06-29ubuntu
redhatunbound-main-1.25.1-1.hum12026-05-23redhat

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.

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 8× in last 7d / 40× 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 121 total refreshes for this CVE.

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

Frequently asked(5)

What is CVE-2026-42923?
CVE-2026-42923 is a medium vulnerability published on May 20, 2026. NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the…
When was CVE-2026-42923 disclosed?
CVE-2026-42923 was first published in the National Vulnerability Database on May 20, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-42923 actively exploited?
CVE-2026-42923 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 26.3% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-42923?
CVE-2026-42923 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-42923?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-42923, 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.

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