FKIE_CVE-2026-41637

Vulnerability from fkie_nvd - Published: 2026-07-22 14:17 - Updated: 2026-07-22 20:33
Severity
3.7 (Low) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
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.
References
sep@nlnetlabs.nlhttps://www.nlnetlabs.nl/downloads/unbound/CVE-2026-41637.txt
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Unbound",
          "vendor": "NLnet Labs",
          "versions": [
            {
              "lessThan": "1.25.2",
              "status": "affected",
              "version": "1.22.0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "source": "sep@nlnetlabs.nl"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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 (\u0027--with-libngtcp2\u0027) and the \u0027quic-port\u0027 to be configured for the listening interfaces. Additionally, a malicious actor needs access to multiple source IPs to bypass the by-default configured \u0027wait-limit\u0027 option."
    }
  ],
  "id": "CVE-2026-41637",
  "lastModified": "2026-07-22T20:33:11.590",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "LOW",
          "baseScore": 3.7,
          "baseSeverity": "LOW",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L",
          "version": "3.1"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 1.4,
        "source": "sep@nlnetlabs.nl",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-41637",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-07-22T14:29:10.891526Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-07-22T14:17:18.560",
  "references": [
    {
      "source": "sep@nlnetlabs.nl",
      "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-41637.txt"
    }
  ],
  "sourceIdentifier": "sep@nlnetlabs.nl",
  "vulnStatus": "Undergoing Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-772"
        }
      ],
      "source": "sep@nlnetlabs.nl",
      "type": "Secondary"
    }
  ]
}



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