Security advisory

{
  "id": "4065d9e7a565b866c25940f9c969e6e1b518978594c62bf146361a60dec64582",
  "url": "https://osv.dev/vulnerability/CVE-2026-55717",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "CVE-2026-55717",
    "summary": "In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'response-ip: redirect' /'response-ip-data: CNAME ' rule (or the RPZ 'rpz-cname-override' equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets 'alias_rrset' but not 'partial_rep'. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of 'serve-expired-client-timeout' is taken leading to denial of service via the server crash.",
    "evidence": "osv:CVE-2026-55717",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-55717",
      "aliases": [
        "CVE-2026-55717"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/nlnetlabs/unbound",
              "type": "GIT",
              "events": [
                {
                  "introduced": "6e7717986b25a48952ebb18e131d6eaa005a9757"
                },
                {
                  "fixed": "c33ad1b1a21e48bfe4f140e90252a9be1b0c5745"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.10.0"
                      },
                      {
                        "fixed": "1.25.2"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55717.json"
          }
        }
      ],
      "modified": "2026-10-26T02:30:56.853092564Z",
      "provider": "osv",
      "references": [
        "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55717.txt"
      ],
      "provider_metadata": {}
    },
    "related_cves": [
      {
        "value": "CVE-2026-55717",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 446682,
  "published_at": "2026-07-22T14:17:21.537+00:00"
}