{"id":"CVE-2026-32665","title":"Remote DNS-over-QUIC denial of service due to `quic-size` budget bypass","summary":"In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, when downstream DNS-over-QUIC (DoQ) is enabled, the first two bidirectional streams on a new QUIC connection (stream_id 0 and 4) bypass the per-stream 'quic-size' gate entirely, an…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cvssSource":"cna","cwe":["CWE-1284"],"vendor":"NLnet Labs","product":"Unbound","affected":["Unbound >= 1.22.0 < 1.25.2"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-07-22T14:31:54.691586Z"},"published":"2026-07-22","updated":"2026-09-16","sourceUpdated":"2026-09-16T14:24:37.708Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-32665","references":[{"url":"https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-32665.txt"}],"tags":["cve.org"],"epss":0.00285,"epssPercentile":0.21205,"ingestedAt":"2026-09-16T14:57:28.057Z","slug":"CVE-2026-32665","body":"## Overview\n\nIn NLnet Labs Unbound 1.22.0 up to and including 1.25.1, when downstream DNS-over-QUIC (DoQ) is enabled, the first two bidirectional streams on a new QUIC connection (stream_id 0 and 4) bypass the per-stream 'quic-size' gate entirely, and large input buffers are allocated later, after only the 2-byte length prefix has been received from the initial streams. As a result, a remote client can make Unbound exceed the configured 'quic-size' limit with low-cost input. Using only one connection and two streams, each sending a declared 65535-byte length prefix and then holding the streams open, a client can already trivially make Unbound roughly allocate double that amount. This is a remote availability issue / memory-accounting bypass in the downstream DoQ implementation that leads to denial of service for new DoQ clients. This vulnerability needs Unbound to be compiled with DoQ support ('--with-libngtcp2') and the 'quic-port' to be configured for the listening interfaces.\n\n## Affected\n\n- `Unbound >= 1.22.0 < 1.25.2`\n\n## Remediation\n\nThis issue is fixed starting with version 1.25.2","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}