Vulnerability-Lookup

FKIE_CVE-2026-77955

Vulnerability from fkie_nvd - Published: 2026-09-16 09:17 - Updated: 2026-09-16 19:41

Severity

4.4 (Medium) - CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:N

Summary

In NLnet Labs Unbound 1.13.2 up to and including 1.26.1, a vulnerability in ZONEMD configured zones (zonemd-check: yes) which are located below (but not at) a trust anchor allow for an attack window where (tampered with) zone contents are served (or stored to disk) prior to the ZONEMD integrity check. This is caused by the needed DS/DNSKEY asynchronous resolution that needs to happen before the ZONEMD check completes. If a zonefile is written to disk (zonefile: option) while the ZONEMD check failed, the tampered data are reloaded on startup and available until ZONEMD verification concludes again. If verification fails, the data is not served any more but still persists on disk for future reloads.

References

	URL	Tags
	sep@nlnetlabs.nl	https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-77955.txt

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Unbound",
          "vendor": "NLnet Labs",
          "versions": [
            {
              "lessThan": "1.26.1",
              "status": "affected",
              "version": "1.13.2",
              "versionType": "semver"
            }
          ]
        }
      ],
      "source": "sep@nlnetlabs.nl"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In NLnet Labs Unbound 1.13.2 up to and including 1.26.1, a vulnerability in ZONEMD configured zones (zonemd-check: yes) which are located below (but not at) a trust anchor allow for an attack window where (tampered with) zone contents are served (or stored to disk) prior to the ZONEMD integrity check. This is caused by the needed DS/DNSKEY asynchronous resolution that needs to happen before the ZONEMD check completes. If a zonefile is written to disk (zonefile: option) while the ZONEMD check failed, the tampered data are reloaded on startup and available until ZONEMD verification concludes again. If verification fails, the data is not served any more but still persists on disk for future reloads."
    }
  ],
  "id": "CVE-2026-77955",
  "lastModified": "2026-09-16T19:41:10.423",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 4.4,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "HIGH",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 0.7,
        "impactScore": 3.6,
        "source": "sep@nlnetlabs.nl",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-77955",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-09-16T14:33:18.720420Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-09-16T09:17:05.780",
  "references": [
    {
      "source": "sep@nlnetlabs.nl",
      "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-77955.txt"
    }
  ],
  "sourceIdentifier": "sep@nlnetlabs.nl",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-345"
        }
      ],
      "source": "sep@nlnetlabs.nl",
      "type": "Secondary"
    }
  ]
}

CVE-2026-77955 (GCVE-0-2026-77955)

Vulnerability from cvelistv5 – Published: 2026-09-16 08:29 – Updated: 2026-09-16 14:33

Title

Possible ZONEMD verification bypass window

Summary

Severity

4.4 (Medium)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-16 14:33 UTC

CWE

CWE-345 - Insufficient Verification of Data Authenticity

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: 1.13.2 , < 1.26.1 (semver)

Date Public

2026-09-16 00:00

Credits

Yuqi Qiu (Nankai University, AOSP Lab) Xiang Li (Nankai University, AOSP Lab) Qifan Zhang (Palo Alto Networks)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-77955",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-16T14:33:18.720420Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-09-16T14:33:24.961Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Unbound",
          "vendor": "NLnet Labs",
          "versions": [
            {
              "lessThan": "1.26.1",
              "status": "affected",
              "version": "1.13.2",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Yuqi Qiu (Nankai University, AOSP Lab)"
        },
        {
          "lang": "en",
          "type": "finder",
          "value": "Xiang Li (Nankai University, AOSP Lab)"
        },
        {
          "lang": "en",
          "type": "finder",
          "value": "Qifan Zhang (Palo Alto Networks)"
        }
      ],
      "datePublic": "2026-09-16T00:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "value": "In NLnet Labs Unbound 1.13.2 up to and including 1.26.1, a vulnerability in ZONEMD configured zones (zonemd-check: yes) which are located below (but not at) a trust anchor allow for an attack window where (tampered with) zone contents are served (or stored to disk) prior to the ZONEMD integrity check. This is caused by the needed DS/DNSKEY asynchronous resolution that needs to happen before the ZONEMD check completes. If a zonefile is written to disk (zonefile: option) while the ZONEMD check failed, the tampered data are reloaded on startup and available until ZONEMD verification concludes again. If verification fails, the data is not served any more but still persists on disk for future reloads."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 4.4,
            "baseSeverity": "MEDIUM",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:N",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "\u0027zonemd-check: yes\u0027 configured for authoritative zones"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-345",
              "description": "CWE-345: Insufficient Verification of Data Authenticity",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-16T08:29:39.955Z",
        "orgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
        "shortName": "NLnet Labs"
      },
      "references": [
        {
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-77955.txt"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "This issue is fixed starting with version 1.26.1"
        }
      ],
      "timeline": [
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          "lang": "en",
          "time": "2026-08-11T00:00:00.000Z",
          "value": "Issue reported by Yuqi Qiu"
        },
        {
          "lang": "en",
          "time": "2026-08-16T00:00:00.000Z",
          "value": "Issue reported by Qifan Zhang"
        },
        {
          "lang": "en",
          "time": "2026-08-19T00:00:00.000Z",
          "value": "NLnet Labs shares patch with Yuqi Qiu"
        },
        {
          "lang": "en",
          "time": "2026-08-20T00:00:00.000Z",
          "value": "Yuqi Qiu verifies patch"
        },
        {
          "lang": "en",
          "time": "2026-09-01T00:00:00.000Z",
          "value": "NLnet Labs shares patch with Qifan Zhang"
        },
        {
          "lang": "en",
          "time": "2026-09-16T00:00:00.000Z",
          "value": "Fixes released with version 1.26.1"
        }
      ],
      "title": "Possible ZONEMD verification bypass window",
      "x_generator": {
        "engine": "cvelib 1.8.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
    "assignerShortName": "NLnet Labs",
    "cveId": "CVE-2026-77955",
    "datePublished": "2026-09-16T08:29:39.955Z",
    "dateReserved": "2026-09-07T14:06:21.947Z",
    "dateUpdated": "2026-09-16T14:33:24.961Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

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