Security advisory

{
  "id": "362c45794745c3eebc0bdbecf4529de9548ae115fd232c63182f71ee768efb2b",
  "url": "https://osv.dev/vulnerability/CVE-2026-41637",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "CVE-2026-41637",
    "summary": "In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, client terminated DNS-over-QUIC (DoQ) queries are not accounted properly by Unbound resulting in low-cost inflation of the waiting number of replies for already in-flight resolution queries. This results in degradation of resolution service for new clients for already in-flight queries. A malicious actor can exploit the vulnerability by issuing DoQ queries for query names that need resolution and proceeding on immediately terminating the query by one of STOP_SENDING/RESET_STREAM/CONNECTION_CLOSE QUIC frames. Those terminated DoQ queries are not properly counted for and keep inflating the number of waiting replies for in-flight queries. When the maximum is reached, it results in silent query drops for new clients needing resolution for already in-flight queries. This vulnerability needs Unbound to be compiled with DoQ support ('--with-libngtcp2') and the 'quic-port' to be configured for the listening interfaces. Additionally, a malicious actor needs access to multiple source IPs to bypass the by-default configured 'wait-limit' option.",
    "evidence": "osv:CVE-2026-41637",
    "products": [],
    "severity": "low",
    "structured": {
      "id": "CVE-2026-41637",
      "aliases": [
        "CVE-2026-41637"
      ],
      "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": "0076736fc40298eb6252705e6e158462c6b24d06"
                },
                {
                  "fixed": "c33ad1b1a21e48bfe4f140e90252a9be1b0c5745"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.22.0"
                      },
                      {
                        "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"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-41637.json"
          }
        }
      ],
      "modified": "2026-10-26T02:30:15.476305389Z",
      "provider": "osv",
      "references": [
        "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-41637.txt"
      ],
      "provider_metadata": {}
    },
    "related_cves": [
      {
        "value": "CVE-2026-41637",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 446625,
  "published_at": "2026-07-22T14:17:18.56+00:00"
}