CVE-2026-41637 (GCVE-0-2026-41637)

Vulnerability from cvelistv5 – Published: 2026-07-22 13:04 – Updated: 2026-07-22 14:29
VLAI
Title
Degradation of resolution service from improperly accounted client-terminated DNS-over-QUIC queries
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.
Severity
3.7 (Low)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-22 14:29 UTC
CWE
  • CWE-772 - Missing Release of Resource after Effective Lifetime
Assigner
References
Impacted products
Vendor Product Version CPE status
NLnet Labs Unbound Affected: 1.22.0 , < 1.25.2 (semver)
guessed Create a notification for this product.
Date Public
2026-07-22 00:00
Credits
Qifan Zhang (Palo Alto Networks)
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-41637",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-07-22T14:29:10.891526Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-07-22T14:29:25.088Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Unbound",
          "vendor": "NLnet Labs",
          "versions": [
            {
              "lessThan": "1.25.2",
              "status": "affected",
              "version": "1.22.0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Qifan Zhang (Palo Alto Networks)"
        }
      ],
      "datePublic": "2026-07-22T00:00:00.000Z",
      "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 3.7,
            "baseSeverity": "LOW",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "Unbound compiled with DoQ support (\u0027--with-libngtcp2\u0027)"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-772",
              "description": "CWE-772: Missing Release of Resource after Effective Lifetime",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-22T13:04:52.605Z",
        "orgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
        "shortName": "NLnet Labs"
      },
      "references": [
        {
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-41637.txt"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "This issue is fixed starting with version 1.25.2"
        }
      ],
      "timeline": [
        {
          "lang": "en",
          "time": "2026-05-22T00:00:00.000Z",
          "value": "Issue reported by Qifan Zhang"
        },
        {
          "lang": "en",
          "time": "2026-06-17T00:00:00.000Z",
          "value": "NLnet Labs shares patch"
        },
        {
          "lang": "en",
          "time": "2026-06-17T00:00:00.000Z",
          "value": "Qifan Zhang verifies patch"
        },
        {
          "lang": "en",
          "time": "2026-07-22T00:00:00.000Z",
          "value": "Fixes released with version 1.25.2"
        }
      ],
      "title": "Degradation of resolution service from improperly accounted client-terminated DNS-over-QUIC queries",
      "x_generator": {
        "engine": "cvelib 1.8.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
    "assignerShortName": "NLnet Labs",
    "cveId": "CVE-2026-41637",
    "datePublished": "2026-07-22T13:04:52.605Z",
    "dateReserved": "2026-06-22T10:11:10.518Z",
    "dateUpdated": "2026-07-22T14:29:25.088Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-41637",
      "date": "2026-09-21",
      "epss": "0.00265",
      "percentile": "0.18689"
    },
    "microsoft_vex": {
      "current_release_date": "2026-07-23T14:45:04.000Z",
      "cve": "CVE-2026-41637",
      "id": "msrc_CVE-2026-41637",
      "initial_release_date": "2026-07-23T01:05:22.000Z",
      "product_status:fixed": "1",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "Degradation of resolution service from improperly accounted client-terminated DNS-over-QUIC queries",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-41637.json",
      "version": "2"
    },
    "nvd": {
      "cve": {
        "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"
          }
        ],
        "configurations": [
          {
            "nodes": [
              {
                "cpeMatch": [
                  {
                    "criteria": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*",
                    "matchCriteriaId": "0C48102E-1D81-4A87-898D-F1CE83C78D26",
                    "versionEndExcluding": "1.25.2",
                    "versionStartIncluding": "1.22.0",
                    "vulnerable": true
                  }
                ],
                "negate": false,
                "operator": "OR"
              }
            ]
          }
        ],
        "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": "2026-07-24T13:57:04.917",
        "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",
            "tags": [
              "Vendor Advisory"
            ],
            "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-41637.txt"
          }
        ],
        "sourceIdentifier": "sep@nlnetlabs.nl",
        "vulnStatus": "Analyzed",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-772"
              }
            ],
            "source": "sep@nlnetlabs.nl",
            "type": "Secondary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-09-01T12:58:54+00:00",
      "cve": "CVE-2026-41637",
      "id": "CVE-2026-41637",
      "initial_release_date": "2026-07-22T13:04:52.605000+00:00",
      "product_status:fixed": "4",
      "product_status:known_affected": "16",
      "product_status:known_not_affected": "15",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "unbound: Unbound: Denial of Service via terminated DNS-over-QUIC queries",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-41637.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-11T01:23:51Z",
      "cve": "CVE-2026-41637",
      "id": "CVE-2026-41637",
      "initial_release_date": "2026-07-26T23:32:22Z",
      "product_status:known_not_affected": "144",
      "product_status:recommended": "28",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-41637",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-41637.json",
      "version": "8"
    },
    "vulnrichment": {
      "containers": {
        "adp": [
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2026-41637",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-07-22T14:29:10.891526Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-07-22T14:29:17.367Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "defaultStatus": "unaffected",
              "product": "Unbound",
              "vendor": "NLnet Labs",
              "versions": [
                {
                  "lessThan": "1.25.2",
                  "status": "affected",
                  "version": "1.22.0",
                  "versionType": "semver"
                }
              ]
            }
          ],
          "credits": [
            {
              "lang": "en",
              "type": "finder",
              "value": "Qifan Zhang (Palo Alto Networks)"
            }
          ],
          "datePublic": "2026-07-22T00:00:00.000Z",
          "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."
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "baseScore": 3.7,
                "baseSeverity": "LOW",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L",
                "version": "3.1"
              },
              "format": "CVSS",
              "scenarios": [
                {
                  "lang": "en",
                  "value": "Unbound compiled with DoQ support (\u0027--with-libngtcp2\u0027)"
                }
              ]
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-772",
                  "description": "CWE-772: Missing Release of Resource after Effective Lifetime",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-07-22T13:04:52.605Z",
            "orgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
            "shortName": "NLnet Labs"
          },
          "references": [
            {
              "tags": [
                "vendor-advisory"
              ],
              "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-41637.txt"
            }
          ],
          "solutions": [
            {
              "lang": "en",
              "value": "This issue is fixed starting with version 1.25.2"
            }
          ],
          "timeline": [
            {
              "lang": "en",
              "time": "2026-05-22T00:00:00.000Z",
              "value": "Issue reported by Qifan Zhang"
            },
            {
              "lang": "en",
              "time": "2026-06-17T00:00:00.000Z",
              "value": "NLnet Labs shares patch"
            },
            {
              "lang": "en",
              "time": "2026-06-17T00:00:00.000Z",
              "value": "Qifan Zhang verifies patch"
            },
            {
              "lang": "en",
              "time": "2026-07-22T00:00:00.000Z",
              "value": "Fixes released with version 1.25.2"
            }
          ],
          "title": "Degradation of resolution service from improperly accounted client-terminated DNS-over-QUIC queries",
          "x_generator": {
            "engine": "cvelib 1.8.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
        "assignerShortName": "NLnet Labs",
        "cveId": "CVE-2026-41637",
        "datePublished": "2026-07-22T13:04:52.605Z",
        "dateReserved": "2026-06-22T10:11:10.518Z",
        "dateUpdated": "2026-07-22T14:29:25.088Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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.



Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.