{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:messagepack:messagepack:*:*:*:*:*:c\\#:*:*",
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "2.5.301"
              },
              {
                "introduced": "3.0.3"
              },
              {
                "fixed": "3.1.7"
              }
            ],
            "source": "CPE_RANGE"
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5657b1e34ea2869a2ca6bc0aa6617158620201ba"
            },
            {
              "introduced": "ff3af77f546138d9da71707baddf2c30f55dfc15"
            },
            {
              "fixed": "1b53ae8b7681340199faf337bcbb0eb5aed702de"
            }
          ],
          "repo": "https://github.com/messagepack-csharp/messagepack-csharp",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-2x83-8g95-xh59"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-407"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48511.json"
  },
  "details": "MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, ExpandoObjectFormatter.Deserialize populates System.Dynamic.ExpandoObject by calling IDictionary\u003cstring, object\u003e.Add for each map entry. ExpandoObject internally maintains member names in array-like structures, so inserting many distinct keys can require repeated linear scans and array copies. For large attacker-controlled maps, this produces quadratic CPU and allocation behavior. The issue is especially surprising because ExpandoObjectResolver.Options is configured with MessagePackSecurity.UntrustedData, but collision-resistant dictionary comparers cannot protect ExpandoObject insertion internals. This vulnerability is fixed in 2.5.301 and 3.1.7.",
  "id": "CVE-2026-48511",
  "modified": "2026-07-15T01:48:58.130788748Z",
  "published": "2026-06-22T21:14:54.127Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48511.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-2x83-8g95-xh59"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-48511"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "MessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted maps"
}