{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "last_affected": "7.0.1"
              }
            ],
            "source": "AFFECTED_FIELD"
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "1be50ee5dadc4b85f79945c51df362582ccb2631"
            }
          ],
          "repo": "https://github.com/msgpack/msgpack-c",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "VulnCheck",
    "cwe_ids": [
      "CWE-190",
      "CWE-787"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72854.json"
  },
  "details": "msgpack_unpacker_expand_buffer in src/unpack.c, reached through the public msgpack_unpacker_reserve_buffer API, computes its new buffer size using an unchecked size_t addition of the requested size and the amount already used. The doubling loop guards its own multiplication against overflow, but the addition in the loop condition is unguarded, so a request near SIZE_MAX wraps: the loop condition is already satisfied, the allocation is performed at the small pre-wrap size, and the function returns true. The caller is told the requested capacity was reserved when it was not, so a subsequent write of the requested length overflows the heap buffer. The library's own example/lib_buffer_unpack.c demonstrates the reserve-then-write pattern, and its defensive assert comparing capacity against the request is compiled out under NDEBUG. msgpack-c's own decode entry points do not derive the reservation size from untrusted input, so reaching this requires an integration that passes an attacker-influenced length to the reservation API, such as a length-prefixed streaming transport.",
  "id": "CVE-2026-72854",
  "modified": "2026-08-22T03:31:00.850346358Z",
  "published": "2026-08-20T18:19:24.266Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72854.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72854"
    },
    {
      "type": "ADVISORY",
      "url": "https://www.vulncheck.com/advisories/msgpack-c-integer-overflow-in-msgpack-unpacker-expand-buffer-causes-a-false-success-undersized-reservation"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/msgpack/msgpack-c/issues/1181"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/msgpack/msgpack-c"
    },
    {
      "type": "ARTICLE",
      "url": "https://github.com/msgpack/msgpack-c/blob/c-7.0.1/example/lib_buffer_unpack.c"
    },
    {
      "type": "ARTICLE",
      "url": "https://github.com/msgpack/msgpack-c/blob/c-7.0.1/include/msgpack/unpack.h#L219-L223"
    },
    {
      "type": "ARTICLE",
      "url": "https://github.com/msgpack/msgpack-c/blob/c-7.0.1/src/unpack.c#L429-L502"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "msgpack-c Integer Overflow in msgpack_unpacker_expand_buffer Causes a False-Success Undersized Reservation"
}