{"id":"CVE-2026-78227","state":"PUBLISHED","title":"Use-after-free in DoQ stream output buffer on reset re-transmission","description":"NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'. Each DoQ stream owns an output buffer that holds the DNS response. ngtcp2's retransmission buffer keeps a shallow pointer into the output buffer for as long as a STREAM frame may be resent. On a client RESET_STREAM, the output buffer is freed but ngtcp2 still holds the matching retransmission entries. The next PTO timeout makes ngtcp2 re-encode the STREAM frame and copy from the freed buffer. A malicious actor that can query Unbound over DoQ and that withholds ACKs, sends RESET_STREAM, and waits for PTO, reaches this use-after-free with no privilege. This leads to retransmissions against freed memory and eventually an abnormal server exit under a 20-query spray.","publishedAt":"2026-09-16T08:29:52.342Z","updatedAt":"2026-09-16T15:33:54.267Z","severity":{"score":6.5,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/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":"1.26.1","versionType":"semver"}]}],"references":["https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-78227.txt"],"weaknesses":["CWE-416"],"ingestedAt":"2026-10-29T20:13:07.220Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/78xxx/CVE-2026-78227.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-78227","state":"PUBLISHED","datePublished":"2026-09-16T08:29:52.342Z","dateUpdated":"2026-09-16T15:33:54.267Z","assignerShortName":"NLnet Labs","assignerOrgId":"206fc3a0-e175-490b-9eaa-a5738056c9f6","dateReserved":"2026-09-07T14:06:21.963Z"},"containers":{"cna":{"title":"Use-after-free in DoQ stream output buffer on reset re-transmission","descriptions":[{"lang":"en","value":"NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'. Each DoQ stream owns an output buffer that holds the DNS response. ngtcp2's retransmission buffer keeps a shallow pointer into the output buffer for as long as a STREAM frame may be resent. On a client RESET_STREAM, the output buffer is freed but ngtcp2 still holds the matching retransmission entries. The next PTO timeout makes ngtcp2 re-encode the STREAM frame and copy from the freed buffer. A malicious actor that can query Unbound over DoQ and that withholds ACKs, sends RESET_STREAM, and waits for PTO, reaches this use-after-free with no privilege. This leads to retransmissions against freed memory and eventually an abnormal server exit under a 20-query spray."}],"affected":[{"vendor":"NLnet Labs","product":"Unbound","defaultStatus":"unaffected","versions":[{"version":"1.22.0","status":"affected","lessThan":"1.26.1","versionType":"semver"}]}],"references":[{"url":"https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-78227.txt","tags":["vendor-advisory"]}],"metrics":[{"format":"CVSS","scenarios":[{"lang":"en","value":"compiled with DNS-over-QUIC support"}],"cvssV3_1":{"version":"3.1","baseScore":6.5,"baseSeverity":"MEDIUM","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:L"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-416","lang":"en","description":"CWE-416: Use After Free","type":"CWE"}]}],"providerMetadata":{"shortName":"NLnet Labs","orgId":"206fc3a0-e175-490b-9eaa-a5738056c9f6","dateUpdated":"2026-09-16T08:29:52.342Z"},"datePublic":"2026-09-16T00:00:00.000Z","solutions":[{"lang":"en","value":"This issue is fixed starting with version 1.26.1"}],"timeline":[{"time":"2026-08-11T00:00:00.000Z","lang":"en","value":"Issue reported by Yuqi Qiu"},{"time":"2026-08-13T00:00:00.000Z","lang":"en","value":"NLnet Labs shares patch"},{"time":"2026-08-14T00:00:00.000Z","lang":"en","value":"Yuqi Qiu verifies patch"},{"time":"2026-09-16T00:00:00.000Z","lang":"en","value":"Fixes released with version 1.26.1"}],"credits":[{"lang":"en","value":"Yuqi Qiu (Nankai University, AOSP Lab)","type":"finder"},{"lang":"en","value":"Xiang Li (Nankai University, AOSP Lab)","type":"finder"}],"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-16T15:33:40.171223Z","id":"CVE-2026-78227","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":"2026-09-16T15:33:54.267Z"}}]}}}