{"id":"CVE-2026-5856","title":"Contiki-NG's DNS/mDNS resolver skip_name() in os/services/resolv/resolv.c walks DNS wire-format name labels with no packet-boundary check, and the caller in newdata() invokes it in a loop iterating nquestions times from the attacker-cont…","summary":"Contiki-NG's DNS/mDNS resolver skip_name() in os/services/resolv/resolv.c walks DNS wire-format name labels with no packet-boundary check, and the caller in newdata() invokes it in a loop iterating nquestions times from the attacker-cont…","severity":"high","cvss":7.1,"cvssVector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L","cwe":["CWE-125"],"published":"2026-08-06","updated":"2026-09-16","sourceUpdated":"2026-09-16T20:21:01.047","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-5856","references":[{"url":"https://github.com/contiki-ng/contiki-ng","label":"disclosure@vulncheck.com"},{"url":"https://github.com/contiki-ng/contiki-ng/commit/04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe","label":"disclosure@vulncheck.com"},{"url":"https://github.com/contiki-ng/contiki-ng/pull/3169","label":"disclosure@vulncheck.com"}],"tags":["nvd"],"epss":0.00253,"epssPercentile":0.17102,"ingestedAt":"2026-09-16T21:05:36.835Z","slug":"CVE-2026-5856","body":"## Overview\n\nContiki-NG's DNS/mDNS resolver skip_name() in os/services/resolv/resolv.c walks DNS wire-format name labels with no packet-boundary check, and the caller in newdata() invokes it in a loop iterating nquestions times from the attacker-controlled DNS header before validating the transaction ID. An attacker who sets nquestions higher than the number of complete questions present causes skip_name() to walk past the UDP packet buffer, and the returned pointer is cast to struct dns_answer * for further memory reads. On builds with RESOLV_CONF_SUPPORTS_MDNS enabled, any peer on the local segment can trigger the read unauthenticated via a multicast UDP 5353 packet with no outstanding query required; on standard DNS builds an attacker who can inject a UDP response from port 53 during an outstanding query can trigger the same read. Impact is out-of-bounds read of uip_buf and adjacent memory, disclosing memory contents or crashing the resolver.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":39,"depthScoreParts":{"impact":39.1,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}