{"id":"CVE-2026-48511","summary":"MessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted maps","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.","aliases":["GHSA-2x83-8g95-xh59"],"modified":"2026-07-15T01:48:58.130788748Z","published":"2026-06-22T21:14:54.127Z","database_specific":{"cwe_ids":["CWE-407"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48511.json","cna_assigner":"GitHub_M"},"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"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/messagepack-csharp/messagepack-csharp","events":[{"introduced":"0"},{"fixed":"5657b1e34ea2869a2ca6bc0aa6617158620201ba"},{"introduced":"ff3af77f546138d9da71707baddf2c30f55dfc15"},{"fixed":"1b53ae8b7681340199faf337bcbb0eb5aed702de"}],"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"}}],"versions":["v3.1.6","v3.1.5","v2.5.198","v3.1.4","v3.1.3","v3.1.2","v3.1.1","v3.1.0","v3.0.301","v3.0.300","v3.0.3","v2.5.192","v2.5.187","v2.5.172","v2.5.171","v2.5.168","v2.5.140","v2.5.129","v2.5.108","v2.5.124","v2.5.103","v2.4.59","v2.5.94","v2.4.35","v2.4.23-alpha","v2.3.85","v2.1.115","v2.3.75","v2.2.113","v2.2.85","v2.2.60","v2.1.194","v2.1.165","v2.1.152","v2.1.143","v2.1.90","v2.1.80","v2.0.270-rc","v2.0.204-beta","v2.0.123-beta","v2.0.119-beta","v2.0.110-alpha","v2.0.94-alpha","v1.7.3.4","v1.7.3.3","v1.7.3.2","v1.7.3.1","v1.7.3","v1.7.2","v1.7.0","v1.6.2","v1.6.1.2","v1.6.1","v1.6.0","v1.5.1","v1.5.0","v1.4.4","v1.4.2","v1.4.1","v1.4.0","v1.3.3","v1.3.2","v1.3.1","v1.3.0","v1.2.3","v1.2.1","v1.2.0","v1.1.2","v1.1.1","v1.0.3","v1.0.2","1.0.1","0.2.0-beta","0.1.0-beta"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-48511.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","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"}]}