MessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted maps_CVE-2026-48511

{
    "lastseen": "",
    "description": "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<string, object>.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.",
    "published": "2026-06-22T21:14:54.127Z",
    "modified": "2026-06-22T21:14:54.127Z",
    "type": "cve",
    "title": "MessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted maps",
    "source": "GitHub_M",
    "references": "https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-2x83-8g95-xh59",
    "id": "CVE-2026-48511",
    "bulletinFamily": "",
    "cwe": [
        "CWE-407"
    ],
    "cvelist": null,
    "sourceData": "MessagePack-CSharp MessagePack-CSharp >= 3.1.7, < 3.1.7\nMessagePack-CSharp MessagePack-CSharp < 2.5.301",
    "sourceHref": "",
    "cvss": {
        "score": 6.3,
        "severity": "MEDIUM",
        "vector": "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",
        "version": "4.0"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
            "attackComplexity": "",
            "privilegesRequired": "",
            "userInteraction": "",
            "scope": "",
            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "MessagePack-CSharp",
    "version": ">= 3.1.7, < 3.1.7",
    "vendor": "MessagePack-CSharp",
    "ai_description": "",
    "ai_severity": "",
    "ai_vendor": "",
    "ai_product": "",
    "ai_version": "",
    "ai_score": 0
}