{"id":"CVE-2026-78227","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-78227","generatedAt":"2026-10-28T00:57:13.983Z","title":"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'.","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.","published":"2026-09-16T09:17:06.000Z","lastModified":"2026-09-23T20:09:02.000Z","status":"Analyzed","sourceIdentifier":"sep@nlnetlabs.nl","cvss":{"version":"3.1","score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:L"},"cwe":["CWE-416"],"affected":["nlnetlabs/unbound"],"epss":{"score":0.0034,"percentile":0.27202,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (0.34%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-78227.txt","tags":["Patch","Vendor Advisory"],"source":"sep@nlnetlabs.nl"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-78227","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}