RIOT has an Out-of-Bounds Write in nanoCoAP Handler

{
  "id": "af5b7b6561ce2b5af35ce4f5e4ae730ada7e6d9e3b051603280b2907552ab8f0",
  "url": "https://osv.dev/vulnerability/CVE-2026-27703",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "RIOT has an Out-of-Bounds Write in nanoCoAP Handler",
    "summary": "RIOT is an open-source microcontroller operating system, designed to match the requirements of Internet of Things (IoT) devices and other embedded devices. In 2026.01 and earlier, the default handler for the well_known_core resource coap_well_known_core_default_handler writes user-provided option data and other data into a fixed size buffer without validating the buffer is large enough to contain the response. This vulnerability allows an attacker to corrupt neighboring stack location, including security-sensitive addresses like the return address, leading to denial of service or arbitrary code execution.",
    "evidence": "osv:CVE-2026-27703",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-27703",
      "aliases": [
        "CVE-2026-27703",
        "GHSA-qgj4-9jff-93cj"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/riot-os/riot",
              "type": "GIT",
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                {
                  "introduced": "0"
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                  "last_affected": "c699e2e20a6c2d0fd45daa766d7a192cb33e579f"
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                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
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          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-27703.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:53.329223864Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27703.json",
        "https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-qgj4-9jff-93cj",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-27703"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-787"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27703.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-27703",
        "evidence": "/id"
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    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 522175,
  "published_at": "2026-03-11T19:38:02.866+00:00"
}