Vulnerability-Lookup

CVE-2026-56416 (GCVE-0-2026-56416)

Vulnerability from cvelistv5 – Published: 2026-07-22 13:10 – Updated: 2026-07-22 14:00

Title

Possible heap buffer overflow when validator canonicalizes RDATA that contains domain name

Summary

In NLnet Labs Unbound up to and including version 1.25.1, when the validator builds the canonical RDATA form for an RRSIG-covered PX/RP/MINFO/SOA RRset, it computes the address of the second embedded domain name as 'datstart + dname_valid(datstart, ...)' and passes it straight to 'query_dname_tolower()' without checking that a second name is actually present in the RDATA. The wire-format parser accepts multi-dname RRs whose RDATA ends after the first name, so an attacker who runs a DNSSEC-signed authoritative server can deliver a record with an absent second domain name (e.g. SOA record) and cause 'query_dname_tolower()' to walk label-by-label through stale bytes in the per-worker 'env->scratch_buffer', past the end of that heap allocation if 'msg-buffer-size' has been lowered from the default. This leads to heap buffer overflow and on a release build the outcome relies heavily on the contents of the buffer tail and the adjacent heap chunk.

Severity

4.8 (Medium)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-354 - Improper Validation of Integrity Check Value

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 , < 1.25.2 (semver)

Date Public

2026-07-22 00:00

Credits

Qifan Zhang (Palo Alto Networks)

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-56416

Vulnerability from fkie_nvd - Published: 2026-07-22 14:17 - Updated: 2026-07-22 15:17

Severity

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

Summary

References

	URL	Tags
	sep@nlnetlabs.nl	https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-56416.txt

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Unbound",
          "vendor": "NLnet Labs",
          "versions": [
            {
              "lessThan": "1.25.2",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "source": "sep@nlnetlabs.nl"
    }
  ],
  "cveTags": [],
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      "lang": "en",
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    }
  ],
  "id": "CVE-2026-56416",
  "lastModified": "2026-07-22T15:17:19.830",
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      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "LOW",
          "baseScore": 4.8,
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          "confidentialityImpact": "NONE",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L",
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        },
        "exploitabilityScore": 2.2,
        "impactScore": 2.5,
        "source": "sep@nlnetlabs.nl",
        "type": "Secondary"
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    ],
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GHSA-2845-97V4-7WM3

Vulnerability from github – Published: 2026-07-22 15:31 – Updated: 2026-07-22 15:31

Details

Severity

4.8 (Medium)


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

Show details on source website

JSON

To clipboard

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  "affected": [],
  "aliases": [
    "CVE-2026-56416"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-354"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-22T14:17:22Z",
    "severity": "MODERATE"
  },
  "details": "In NLnet Labs Unbound up to and including version 1.25.1, when the validator builds the canonical RDATA form for an RRSIG-covered PX/RP/MINFO/SOA RRset, it computes the address of the second embedded domain name as \u0027datstart + dname_valid(datstart, ...)\u0027 and passes it straight to \u0027query_dname_tolower()\u0027 without checking that a second name is actually present in the RDATA. The wire-format parser accepts multi-dname RRs whose RDATA ends after the first name, so an attacker who runs a DNSSEC-signed authoritative server can deliver a record with an absent second domain name (e.g. SOA record) and cause \u0027query_dname_tolower()\u0027 to walk label-by-label through stale bytes in the per-worker \u0027env-\u003escratch_buffer\u0027, past the end of that heap allocation if \u0027msg-buffer-size\u0027 has been lowered from the default. This leads to heap buffer overflow and on a release build the outcome relies heavily on the contents of the buffer tail and the adjacent heap chunk.",
  "id": "GHSA-2845-97v4-7wm3",
  "modified": "2026-07-22T15:31:25Z",
  "published": "2026-07-22T15:31:25Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-56416"
    },
    {
      "type": "WEB",
      "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-56416.txt"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L",
      "type": "CVSS_V3"
    }
  ]
}

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.

Action not permitted

CVE-2026-56416 (GCVE-0-2026-56416)

FKIE_CVE-2026-56416

GHSA-2845-97V4-7WM3

Tags

Sightings

Nomenclature