{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-5856", "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "state": "PUBLISHED", "assignerShortName": "VulnCheck", "dateReserved": "2026-04-08T19:29:07.686Z", "datePublished": "2026-08-06T18:47:38.653Z", "dateUpdated": "2026-08-06T18:47:38.653Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "shortName": "VulnCheck", "dateUpdated": "2026-08-06T18:47:38.653Z"}, "title": "Contiki-NG DNS/mDNS Resolver Out-of-Bounds Read via Unchecked skip_name Traversal Before Transaction-ID Validation", "datePublic": "2026-08-06T19:00:00.000Z", "problemTypes": [{"descriptions": [{"lang": "en", "cweId": "CWE-125", "description": "CWE-125 Out-of-bounds read", "type": "CWE"}]}], "affected": [{"vendor": "Contiki-NG", "product": "Contiki-NG", "versions": [{"status": "affected", "version": "0", "lessThan": "04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe", "versionType": "custom"}], "defaultStatus": "affected"}], "descriptions": [{"lang": "en", "value": "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-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.", "supportingMedia": [{"type": "text/html", "base64": false, "value": "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-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. "}]}], "references": [{"url": "https://github.com/contiki-ng/contiki-ng", "tags": ["product"]}, {"url": "https://github.com/contiki-ng/contiki-ng/pull/3169", "tags": ["issue-tracking"]}, {"url": "https://github.com/contiki-ng/contiki-ng/commit/04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe", "tags": ["patch"]}], "metrics": [{"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV3_1": {"version": "3.1", "attackVector": "ADJACENT_NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "LOW", "baseSeverity": "HIGH", "baseScore": 7.1, "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L"}}, {"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV4_0": {"attackVector": "ADJACENT", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "HIGH", "subConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "subIntegrityImpact": "NONE", "vulnAvailabilityImpact": "LOW", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "version": "4.0", "baseSeverity": "HIGH", "baseScore": 7.1, "vectorString": "CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N"}}], "credits": [{"lang": "en", "value": "Kazuma Matsumoto, a security researcher at GMO Cybersecurity by IERAE, Inc.", "type": "reporter"}], "source": {"discovery": "UNKNOWN"}, "x_generator": {"engine": "vulncheck"}}}}

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