Vulnerability-Lookup

GHSA-8F6W-8H24-FW66

Vulnerability from github – Published: 2026-05-20 12:30 – Updated: 2026-05-21 00:30

Details

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.

Severity ?

5.3 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

6.9 (Medium)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/U:Amber

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{
  "affected": [],
  "aliases": [
    "CVE-2026-42923"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-407"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-20T10:16:27Z",
    "severity": "MODERATE"
  },
  "details": "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.",
  "id": "GHSA-8f6w-8h24-fw66",
  "modified": "2026-05-21T00:30:27Z",
  "published": "2026-05-20T12:30:36Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42923"
    },
    {
      "type": "WEB",
      "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42923.txt"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber",
      "type": "CVSS_V4"
    }
  ]
}

CVE-2026-42923 (GCVE-0-2026-42923)

Vulnerability from cvelistv5 – Published: 2026-05-20 09:20 – Updated: 2026-05-20 12:10

Title

Degradation of service with unbounded NSEC3 hash calculations

Summary

Severity ?

6.9 (Medium)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/U:Amber

CWE

CWE-407 - Inefficient Algorithmic Complexity

Assigner

NLnet Labs

References

1 reference

URL	Tags
https://www.nlnetlabs.nl/downloads/unbound/CVE-20…	vendor-advisory

Impacted products

1 product

Vendor	Product	Version
NLnet Labs	Unbound	Affected: 0 , < 1.25.1 (semver)

Date Public ?

2026-05-20 00:00

Credits

Qifan Zhang (Palo Alto Networks)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-42923",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-20T12:10:04.210764Z",
                "version": "2.0.3"
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          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Unbound",
          "vendor": "NLnet Labs",
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              "version": "0",
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          ]
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      "credits": [
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          "type": "finder",
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      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
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            "baseSeverity": "MEDIUM",
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              "lang": "en",
              "type": "CWE"
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      "providerMetadata": {
        "dateUpdated": "2026-05-20T09:20:01.104Z",
        "orgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
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      },
      "references": [
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          "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42923.txt"
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      ],
      "solutions": [
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          "value": "This issue is fixed starting with version 1.25.1"
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          "time": "2026-04-28T00:00:00.000Z",
          "value": "Issue reported by Qifan Zhang"
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          "time": "2026-05-08T00:00:00.000Z",
          "value": "Qifan Zhang verifies patch"
        },
        {
          "lang": "en",
          "time": "2026-05-20T00:00:00.000Z",
          "value": "Fixes released with version 1.25.1"
        }
      ],
      "title": "Degradation of service with unbounded NSEC3 hash calculations",
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      }
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  },
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    "datePublished": "2026-05-20T09:20:01.104Z",
    "dateReserved": "2026-05-07T10:07:51.800Z",
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    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-8F6W-8H24-FW66

CVE-2026-42923 (GCVE-0-2026-42923)

Tags

Sightings

Nomenclature