{"id":"CVE-2026-41637","state":"PUBLISHED","title":"Degradation of resolution service from improperly accounted client-terminated DNS-over-QUIC queries","description":"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.","publishedAt":"2026-07-22T13:04:52.605Z","updatedAt":"2026-07-22T14:29:25.088Z","severity":{"score":3.7,"label":"Low","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L","source":"NLnet Labs"},"assigner":"NLnet Labs","products":["NLnet Labs Unbound"],"affected":[{"vendor":"NLnet Labs","product":"Unbound","defaultStatus":"unaffected","versions":[{"version":"1.22.0","status":"affected","lessThan":"1.25.2","versionType":"semver"}]}],"references":["https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-41637.txt"],"weaknesses":["CWE-772"],"ingestedAt":"2026-10-29T20:11:57.932Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/41xxx/CVE-2026-41637.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-41637","state":"PUBLISHED","datePublished":"2026-07-22T13:04:52.605Z","dateUpdated":"2026-07-22T14:29:25.088Z","assignerShortName":"NLnet Labs","assignerOrgId":"206fc3a0-e175-490b-9eaa-a5738056c9f6","dateReserved":"2026-06-22T10:11:10.518Z"},"containers":{"cna":{"title":"Degradation of resolution service from improperly accounted client-terminated DNS-over-QUIC queries","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 ('--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."}],"affected":[{"vendor":"NLnet Labs","product":"Unbound","defaultStatus":"unaffected","versions":[{"version":"1.22.0","status":"affected","lessThan":"1.25.2","versionType":"semver"}]}],"references":[{"url":"https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-41637.txt","tags":["vendor-advisory"]}],"metrics":[{"format":"CVSS","scenarios":[{"lang":"en","value":"Unbound compiled with DoQ support ('--with-libngtcp2')"}],"cvssV3_1":{"version":"3.1","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"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-772","lang":"en","description":"CWE-772: Missing Release of Resource after Effective Lifetime","type":"CWE"}]}],"providerMetadata":{"shortName":"NLnet Labs","orgId":"206fc3a0-e175-490b-9eaa-a5738056c9f6","dateUpdated":"2026-07-22T13:04:52.605Z"},"datePublic":"2026-07-22T00:00:00.000Z","solutions":[{"lang":"en","value":"This issue is fixed starting with version 1.25.2"}],"timeline":[{"time":"2026-05-22T00:00:00.000Z","lang":"en","value":"Issue reported by Qifan Zhang"},{"time":"2026-06-17T00:00:00.000Z","lang":"en","value":"NLnet Labs shares patch"},{"time":"2026-06-17T00:00:00.000Z","lang":"en","value":"Qifan Zhang verifies patch"},{"time":"2026-07-22T00:00:00.000Z","lang":"en","value":"Fixes released with version 1.25.2"}],"credits":[{"lang":"en","value":"Qifan Zhang (Palo Alto Networks)","type":"finder"}],"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-07-22T14:29:10.891526Z","id":"CVE-2026-41637","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-07-22T14:29:25.088Z"}}]}}}