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

{
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "cveMetadata": {
    "cveId": "CVE-2026-102715",
    "assignerOrgId": "e51fbebd-6053-4e49-959f-1b94eeb69a2c",
    "assignerShortName": "eclipse",
    "dateUpdated": "2026-09-29T17:42:35.719Z",
    "dateReserved": "2026-09-29T16:15:11.235Z",
    "datePublished": "2026-09-29T17:42:35.719Z",
    "state": "PUBLISHED"
  },
  "containers": {
    "cna": {
      "providerMetadata": {
        "orgId": "e51fbebd-6053-4e49-959f-1b94eeb69a2c",
        "shortName": "eclipse",
        "dateUpdated": "2026-09-29T17:42:35.719Z"
      },
      "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",
      "descriptions": [
        {
          "lang": "en",
          "value": "Any host on the LAN can send two mDNS records and make the responder write past the end of its\n\n\n\ntransmit packet.\n\n\n\nThe string table stores each name in a slot rounded up to a multiple of four:\n\n\n\n```c\n\n\n\n/* addons/mdns/nxd_mdns.c:11436, 11443, 11447 */\n\n\n\nmemory_len = ((memory_len & 0xFFFFFFFC) + 8) & 0xFFFFFFFF;\n\n\n\n...\n\n\n\nlen = *((USHORT*)(p - 2));           /* slot size, not string length */\n\n\n\nif ((len == memory_len) && ... _nx_mdns_name_match(start, memory_ptr, memory_size) ...)\n\n\n\n```\n\n\n\nThe lookup that decides whether an incoming name is already stored compares the rounded slot size,\n\n\n\nso names of 12, 13, 14 and 15 characters share one bucket. A second name in the bucket is answered\n\n\n\nwith the pointer to the first, and the record then carries a string up to three bytes longer than\n\n\n\nthe length the caller accounted for. `_nx_mdns_packet_rr_add` (nxd_mdns.c:8911) sizes its only\n\n\n\nbound check from that stale length, and `_nx_mdns_name_string_encode` writes the real string.\n\n\n\nTwo PTR records are enough, both ordinary mDNS responses to a `_http._tcp` query, with owner names\n\n\n\nwhose lengths fall in the same bucket:\n\n\n\n```\n\n\n\n==87491==ERROR: AddressSanitizer: heap-buffer-overflow\n\n\n\nWRITE of size 1 at 0x611000000124 thread T5\n\n    #0 _nx_mdns_name_string_encode  addons/mdns/nxd_mdns.c:13096\n    #1 _nx_mdns_packet_rr_add       addons/mdns/nxd_mdns.c:8911\n\n\n0x611000000124 is 0 bytes to the right of 228-byte region\n\n\n\n```\n\n\n\nThe overflow is one to three bytes of attacker-influenced name data past `nx_packet_data_end`. In a\n\n\n\nnormal pool that lands in the next packet in the same pool rather than in a redzone, so the visible\n\n\n\neffect is a corrupted neighbouring packet or a corrupted pool free list rather than a clean crash.\n\n\n\nCompare the slot size against the stored string length before declaring a match, or keep the\n\n\n\nstring length in the slot header and return it to the caller so the encoder and the bound check\n\n\n\nagree.",
          "supportingMedia": [
            {
              "type": "text/html",
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              "value": "<p>Any host on the LAN can send two mDNS records and make the responder write past the end of its</p><p>transmit packet.</p><p>The string table stores each name in a slot rounded up to a multiple of four:</p><p>```c</p><p>/* addons/mdns/nxd_mdns.c:11436, 11443, 11447 */</p><p>memory_len = ((memory_len &amp; 0xFFFFFFFC) + 8) &amp; 0xFFFFFFFF;</p><p>...</p><p>len = *((USHORT*)(p - 2));           /* slot size, not string length */</p><p>if ((len == memory_len) &amp;&amp; ... _nx_mdns_name_match(start, memory_ptr, memory_size) ...)</p><p>```</p><p>The lookup that decides whether an incoming name is already stored compares the rounded slot size,</p><p>so names of 12, 13, 14 and 15 characters share one bucket. A second name in the bucket is answered</p><p>with the pointer to the first, and the record then carries a string up to three bytes longer than</p><p>the length the caller accounted for. `_nx_mdns_packet_rr_add` (nxd_mdns.c:8911) sizes its only</p><p>bound check from that stale length, and `_nx_mdns_name_string_encode` writes the real string.</p><p>Two PTR records are enough, both ordinary mDNS responses to a `_http._tcp` query, with owner names</p><p>whose lengths fall in the same bucket:</p><p>```</p><p>==87491==ERROR: AddressSanitizer: heap-buffer-overflow</p><p>WRITE of size 1 at 0x611000000124 thread T5</p><code>    #0 _nx_mdns_name_string_encode  addons/mdns/nxd_mdns.c:13096</code><br><code>    #1 _nx_mdns_packet_rr_add       addons/mdns/nxd_mdns.c:8911</code><br><p>0x611000000124 is 0 bytes to the right of 228-byte region</p><p>```</p><p>The overflow is one to three bytes of attacker-influenced name data past `nx_packet_data_end`. In a</p><p>normal pool that lands in the next packet in the same pool rather than in a redzone, so the visible</p><p>effect is a corrupted neighbouring packet or a corrupted pool free list rather than a clean crash.</p><p>Compare the slot size against the stored string length before declaring a match, or keep the</p><p>string length in the slot header and return it to the caller so the encoder and the bound check</p><p>agree.</p>"
            }
          ]
        }
      ],
      "affected": [
        {
          "vendor": "Eclipse Foundation",
          "product": "eclipse-threadx/netxduo",
          "defaultStatus": "unaffected",
          "versions": [
            {
              "version": "0",
              "status": "affected",
              "versionType": "semver",
              "lessThanOrEqual": "6.5.1"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "lang": "en",
              "description": "CWE-787 Out-of-bounds Write",
              "cweId": "CWE-787",
              "type": "CWE"
            }
          ]
        }
      ],
      "references": [
        {
          "url": "https://github.com/eclipse-threadx/netxduo/security/advisories/GHSA-2gf7-5224-5vrj"
        }
      ],
      "metrics": [
        {
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "value": "L0stHeart",
          "type": "reporter"
        }
      ]
    }
  }
}