Vulnerability-Lookup

GHSA-8M55-G479-XJ8C

Vulnerability from github – Published: 2026-08-07 00:31 – Updated: 2026-08-07 00:31

Details

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.

Severity

7.1 (High)


                  
                    CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L

7.1 (High)


                  
                    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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-5856"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-125"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-06T22:18:10Z",
    "severity": "HIGH"
  },
  "details": "Contiki-NG\u0027s 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.",
  "id": "GHSA-8m55-g479-xj8c",
  "modified": "2026-08-07T00:31:19Z",
  "published": "2026-08-07T00:31:19Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-5856"
    },
    {
      "type": "WEB",
      "url": "https://github.com/contiki-ng/contiki-ng/pull/3169"
    },
    {
      "type": "WEB",
      "url": "https://github.com/contiki-ng/contiki-ng/commit/04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe"
    },
    {
      "type": "WEB",
      "url": "https://github.com/contiki-ng/contiki-ng"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L",
      "type": "CVSS_V3"
    },
    {
      "score": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

CVE-2026-5856 (GCVE-0-2026-5856)

Vulnerability from cvelistv5 – Published: 2026-08-06 18:47 – Updated: 2026-08-07 17:41

Title

Contiki-NG DNS/mDNS Resolver Out-of-Bounds Read via Unchecked skip_name Traversal Before Transaction-ID Validation

Summary

Severity

7.1 (High)


                        
                          CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L

7.1 (High)


                        
                          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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-125 - Out-of-bounds read

Assigner

VulnCheck

References

3 references

URL	Tags
https://github.com/contiki-ng/contiki-ng	product
https://github.com/contiki-ng/contiki-ng/pull/3169	issue-tracking
https://github.com/contiki-ng/contiki-ng/commit/0…	patch

Impacted products

1 product

Vendor	Product	Version
Contiki-NG	Contiki-NG	Affected: 0 , < 04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe (custom)

Date Public

2026-08-06 19:00

Credits

Kazuma Matsumoto, a security researcher at GMO Cybersecurity by IERAE, Inc.

Show details on NVD website

JSON

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{
  "containers": {
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      {
        "metrics": [
          {
            "other": {
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                "id": "CVE-2026-5856",
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                  },
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                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-07T17:40:56.628510Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
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        "providerMetadata": {
          "dateUpdated": "2026-08-07T17:41:09.683Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
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          "defaultStatus": "affected",
          "product": "Contiki-NG",
          "vendor": "Contiki-NG",
          "versions": [
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              "lessThan": "04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe",
              "status": "affected",
              "version": "0",
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      "credits": [
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          "type": "reporter",
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        }
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      "descriptions": [
        {
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          "supportingMedia": [
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              "base64": false,
              "type": "text/html",
              "value": "Contiki-NG\u0027s 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.\u0026nbsp;"
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            "confidentialityImpact": "HIGH",
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            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
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            "vulnerabilityResponseEffort": "NOT_DEFINED"
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      "references": [
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          ],
          "url": "https://github.com/contiki-ng/contiki-ng/pull/3169"
        },
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        }
      ],
      "source": {
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      },
      "title": "Contiki-NG DNS/mDNS Resolver Out-of-Bounds Read via Unchecked skip_name Traversal Before Transaction-ID Validation",
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    "datePublished": "2026-08-06T18:47:38.653Z",
    "dateReserved": "2026-04-08T19:29:07.686Z",
    "dateUpdated": "2026-08-07T17:41:09.683Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

Action not permitted

GHSA-8M55-G479-XJ8C

CVE-2026-5856 (GCVE-0-2026-5856)

Tags

Sightings

Nomenclature