{
    "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": "2026-08-14T16:50:26.963Z"
    },
    "containers": {
        "cna": {
            "providerMetadata": {
                "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
                "shortName": "VulnCheck",
                "dateUpdated": "2026-08-14T16:50:26.963Z"
            },
            "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"
                }
            ],
            "cpeApplicability": [
                {
                    "nodes": [
                        {
                            "operator": "OR",
                            "negate": false,
                            "cpeMatch": [
                                {
                                    "vulnerable": true,
                                    "criteria": "cpe:2.3:o:contiki-ng:contiki-ng:*:*:*:*:*:*:*:*"
                                }
                            ]
                        }
                    ]
                }
            ],
            "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"
            }
        },
        "adp": [
            {
                "metrics": [
                    {
                        "other": {
                            "type": "ssvc",
                            "content": {
                                "timestamp": "2026-08-07T17:40:56.628510Z",
                                "id": "CVE-2026-5856",
                                "options": [
                                    {
                                        "Exploitation": "none"
                                    },
                                    {
                                        "Automatable": "no"
                                    },
                                    {
                                        "Technical Impact": "partial"
                                    }
                                ],
                                "role": "CISA Coordinator",
                                "version": "2.0.3"
                            }
                        }
                    }
                ],
                "title": "CISA ADP Vulnrichment",
                "providerMetadata": {
                    "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
                    "shortName": "CISA-ADP",
                    "dateUpdated": "2026-08-07T17:41:09.683Z"
                }
            }
        ]
    }
}