Security advisory

{
  "id": "93c94db9a43aacbc0b2a21d38ad32c80d7efa918df6f065a50600e96387303e5",
  "url": "https://osv.dev/vulnerability/CVE-2026-44687",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "CVE-2026-44687",
    "summary": "In NLnet Labs Unbound 1.13.2 up to and including 1.25.1, stub or forward zones where the name is below an intermediate labed below a DNSSEC signed zone could be shadowed by the intermediate label's secure NXDOMAIN answer from the parent. This is caused by an off-by-one error in 'harden-below-nxdomain' logic; enabled by default. It effectively bypasses the configuration and the configured stub/forward zone is never contacted. 'harden-below-nxdomain' does an upward DNS cache walk together with a delegation point guard that does not allow NXDOMAIN synthesis above stub/forward zones. The guard tests the domain name but before stripping a label. This results in an iteration where the domain name equals the configured stub/forward zone apex that passes the guard, strips one more label, and probes the cache at the apex's immediate public parent. If that parent has a cached DNSSEC-secure NXDOMAIN, which it will for any private namespace nested two or more labels under a signed public name, the walk returns it and the configured stub/forward upstream is never contacted. This can only be triggered by the query for the intermediate label (between the stub/forward apex and the DNSSEC parent zone).",
    "evidence": "osv:CVE-2026-44687",
    "products": [],
    "severity": "low",
    "structured": {
      "id": "CVE-2026-44687",
      "aliases": [
        "CVE-2026-44687"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/nlnetlabs/unbound",
              "type": "GIT",
              "events": [
                {
                  "introduced": "8e538dcaa8df2d0fab8ff3dcf94ac1f972450b66"
                },
                {
                  "fixed": "c33ad1b1a21e48bfe4f140e90252a9be1b0c5745"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.13.2"
                      },
                      {
                        "fixed": "1.25.2"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "release-1.25.1",
            "release-1.25.0",
            "release-1.25.0rc1",
            "release-1.24.0",
            "release-1.24.0rc1",
            "release-1.23.0rc1",
            "release-1.22.0",
            "release-1.22.0rc1",
            "release-1.21.0",
            "release-1.21.0rc1",
            "release-1.20.0rc1",
            "release-1.20.0",
            "release-1.19.3rc1",
            "release-1.19.0rc1",
            "release-1.19.0",
            "release-1.18.0",
            "release-1.18.0rc1",
            "release-1.16.2",
            "release-1.16.1rc1",
            "release-1.16.1",
            "release-1.16.0rc1",
            "release-1.16.0",
            "release-1.15.0rc1",
            "release-1.15.0",
            "release-1.14.0rc1",
            "release-1.14.0",
            "release-1.13.2"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-44687.json"
          }
        }
      ],
      "modified": "2026-10-26T02:30:27.822978397Z",
      "provider": "osv",
      "references": [
        "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-44687.txt"
      ],
      "provider_metadata": {}
    },
    "related_cves": [
      {
        "value": "CVE-2026-44687",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 446643,
  "published_at": "2026-07-22T14:17:19.04+00:00"
}