mDNS string-cache lookup matches on slot size, so a peer name aliases a shorter one and the response encoder writes past the packet

{
  "id": "27502f5039af299eef534f23088c7ab10843e9e3d7c3f45ec62cac9bb9ca953c",
  "url": "https://osv.dev/vulnerability/CVE-2026-102715",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "mDNS string-cache lookup matches on slot size, so a peer name aliases a shorter one and the response encoder writes past the packet",
    "summary": "Any host on the LAN can send two mDNS records and make the responder write past the end of its transmit packet. The string table stores each name in a slot rounded up to a multiple of four: ```c /* addons/mdns/nxd_mdns.c:11436, 11443, 11447 */ memory_len = ((memory_len & 0xFFFFFFFC) + 8) & 0xFFFFFFFF; ... len = *((USHORT*)(p - 2)); /* slot size, not string length */ if ((len == memory_len) && ... _nx_mdns_name_match(start, memory_ptr, memory_size) ...) ``` The lookup that decides whether an incoming name is already stored compares the rounded slot size, so names of 12, 13, 14 and 15 characters share one bucket. A second name in the bucket is answered with the pointer to the first, and the record then carries a string up to three bytes longer than the length the caller accounted for. `_nx_mdns_packet_rr_add` (nxd_mdns.c:8911) sizes its only bound check from that stale length, and `_nx_mdns_name_string_encode` writes the real string. Two PTR records are enough, both ordinary mDNS responses to a `_http._tcp` query, with owner names whose lengths fall in the same bucket: ``` ==87491==ERROR: AddressSanitizer: heap-buffer-overflow WRITE of size 1 at 0x611000000124 thread T5 #0 _nx_mdns_name_string_encode addons/mdns/nxd_mdns.c:13096 #1 _nx_mdns_packet_rr_add addons/mdns/nxd_mdns.c:8911 0x611000000124 is 0 bytes to the right of 228-byte region ``` The overflow is one to three bytes of attacker-influenced name data past `nx_packet_data_end`. In a normal pool that lands in the next pa",
    "evidence": "osv:CVE-2026-102715",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-102715",
      "aliases": [
        "CVE-2026-102715",
        "GHSA-2gf7-5224-5vrj"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/eclipse-threadx/netxduo",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "last_affected": "1a0e9e43a03e37ddecfb6b49e9b078d6e1803d05"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "last_affected": "6.5.1"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v6.4.1_rel",
            "v6.5.1.202602_rel",
            "v6.5.0.202601_rel",
            "v6.4.5.202504_rel",
            "v6.4.4.202503a",
            "v.6.4.4.202503_rel",
            "v6.4.3_rel",
            "v6.4.2_rel",
            "v6.4.0_rel",
            "v6.3.0_rel",
            "v6.2.1_rel",
            "v6.2.0_rel",
            "v6.1.12_rel",
            "v6.1.11_rel",
            "v6.1.10_rel",
            "v6.1.9_rel",
            "v6.1.8_rel",
            "v6.1.7_rel",
            "v6.1.6_rel",
            "v6.1.5_rel",
            "v6.1.4_rel",
            "v6.1.3_rel",
            "v6.1.2_rel",
            "v6.1_rel",
            "v6.0.2_rel",
            "v6.0.1_rel",
            "v6.0_rel"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-102715.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:27.843473542Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/102xxx/CVE-2026-102715.json",
        "https://github.com/eclipse-threadx/netxduo/security/advisories/GHSA-2gf7-5224-5vrj",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-102715"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-787"
        ],
        "cna_assigner": "eclipse",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/102xxx/CVE-2026-102715.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-102715",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 494282,
  "published_at": "2026-09-29T17:42:35.719+00:00"
}