Vulnerability-Lookup

UBUNTU-CVE-2026-81634 (CVE-2026-81634)

Vulnerability from osv_ubuntu – Published: 2026-09-17 00:00 – Updated: 2026-09-17 00:00 – Source website

Details

In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.

Severity

7.5 (High)


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

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2026-81634	REPORT
	https://www.cve.org/CVERecord?id=CVE-2026-81634	REPORT
	https://nlnetlabs.nl/downloads/unbound/CVE-2026-8…	REPORT
	https://www.nlnetlabs.nl/downloads/unbound/CVE-20…	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "libunbound2",
            "binary_version": "1.4.22-1ubuntu4.14.04.3+esm3"
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            "binary_version": "1.4.22-1ubuntu4.14.04.3+esm3"
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          {
            "binary_name": "unbound",
            "binary_version": "1.4.22-1ubuntu4.14.04.3+esm3"
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      },
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        "1.13.1-1ubuntu5.4",
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        "1.13.1-1ubuntu5.8",
        "1.13.1-1ubuntu5.10",
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            "binary_version": "1.24.2-1ubuntu2.2"
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        ]
      },
      "package": {
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      },
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    }
  ],
  "aliases": [],
  "details": "In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.",
  "id": "UBUNTU-CVE-2026-81634",
  "modified": "2026-09-17T00:00:00Z",
  "published": "2026-09-17T00:00:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-81634"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-81634"
    },
    {
      "type": "REPORT",
      "url": "https://nlnetlabs.nl/downloads/unbound/CVE-2026-81634.txt"
    },
    {
      "type": "REPORT",
      "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-81634.txt"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-81634"
  ]
}

CVE-2026-81634 (GCVE-0-2026-81634)

Vulnerability from cvelistv5 – Published: 2026-09-16 08:30 – Updated: 2026-09-16 14:32

Title

Possible heap buffer overflow during DNSSEC canonicalization

Summary

Severity

7.5 (High)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-16 14:32 UTC

CWE

CWE-122 - Heap-based Buffer Overflow

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 , < 1.26.1 (semver)

Date Public

2026-09-16 00:00

Credits

Vlatko Kosturjak (Marlink Cyber)

Show details on NVD website

JSON

To clipboard

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                  },
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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.

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

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.