{"id":"CVE-2026-55717","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-55717","generatedAt":"2026-10-28T05:59:24.197Z","title":"In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'response-ip: <net> redirect' /'response-ip-data: <net> CNAME <target>' rule (or the RPZ 'rpz-cname-override' equivalent), a remote client who…","description":"In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'response-ip: <net> redirect' /'response-ip-data: <net> CNAME <target>' rule (or the RPZ 'rpz-cname-override' equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets 'alias_rrset' but not 'partial_rep'. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of 'serve-expired-client-timeout' is taken leading to denial of service via the server crash.","published":"2026-07-22T14:17:22.000Z","lastModified":"2026-10-24T13:10:00.000Z","status":"Analyzed","sourceIdentifier":"sep@nlnetlabs.nl","cvss":{"version":"3.1","score":5.9,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H"},"cwe":["CWE-476"],"affected":["nlnetlabs/unbound"],"epss":{"score":0.00237,"percentile":0.14689,"date":"2026-10-27","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 (0.24%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55717.txt","tags":["Vendor Advisory"],"source":"sep@nlnetlabs.nl"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-55717","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."}