{"id":"EM-20261113-IYWF","url":"https://cyber.eventmonitor.net/incident/EM-20261113-IYWF/messagepack-vulnerability-cve-2026-126366/","type":"cve","title":"MessagePack Vulnerability (CVE-2026-126366)","subtitle":"CVE-2026-126366","subject":"CVE-2026-126366","status":"Developing","severity":"high","affected":[],"headline":null,"born":"2026-11-13T00:20:12.397Z","firstSignal":"2026-11-12T22:54:59.000Z","lastSignal":"2026-11-13T00:20:12.397Z","updated":"2026-11-13T00:40:17.050Z","revision":1,"life":[{"status":"Born","at":"2026-11-13T00:20:12.397Z","why":"second independent source: C6 NVD CVE API 2.0"},{"status":"Developing","at":"2026-11-13T00:20:12.397Z","why":"signals keep joining"}],"changeLog":[{"at":"2026-11-12T22:54:59.000Z","what":"First signal: C26 GitHub Advisory Database"},{"at":"2026-11-13T00:20:12.397Z","what":"Born: second source, C6 NVD CVE API 2.0. Page EM-20261113-IYWF created."}],"stages":[{"name":"Disclosed","at":"2026-11-13T00:20:12.397Z","detail":"C6 NVD published"},{"name":"Scored","at":"2026-11-13T00:20:12.397Z","detail":"CVSS 7.5"},{"name":"Exploited","at":null,"detail":"No exploitation reported"},{"name":"Advisories","at":null,"detail":"None yet"},{"name":"Vendor Response","at":null,"detail":"None in sources yet"},{"name":"Resolved","at":null,"detail":"After 14 quiet days"}],"signals":[{"at":"2026-11-12T22:54:59.000Z","source":"C26","sourceName":"GitHub Advisory Database","role":"Database","severity":3,"title":"GHSA-73v3-wf97-vpgj / CVE-2026-126366: msgpack-ruby JRuby decoder makes uncapped header-count allocations; a 5-byte message forces multi-GiB OOM","text":"rubygems:msgpack","url":"https://github.com/advisories/GHSA-73v3-wf97-vpgj"},{"at":"2026-11-13T00:20:12.397Z","source":"C6","sourceName":"NVD CVE API 2.0","role":"Database","severity":3,"title":"CVE-2026-126366 (CVSS 7.5)","text":"MessagePack for Ruby is an implementation of the MessagePack binary serialization format. Prior to 1.8.7, the Java-platform msgpack gem for JRuby allocated arrays and byte buffers directly from attacker-controlled array32, str32, and bin32 declared sizes before confirming that corresponding elements or bytes were available. A short MessagePack header could therefore trigger a very large allocation or sustained heap growth when an application decoded untrusted input through MessagePack.unpack or MessagePack::Unpacker, potentially exhausting the shared JVM heap. map32 and declared counts at or…","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-126366"}],"crowd":[],"reference":{"nvd":{"published":"2026-11-13T00:20:12.397","score":7.5,"severity":"HIGH","desc":"MessagePack for Ruby is an implementation of the MessagePack binary serialization format. Prior to 1.8.7, the Java-platform msgpack gem for JRuby allocated arrays and byte buffers directly from attacker-controlled array32, str32, and bin32 declared sizes before confirming that corresponding…","product":"","seen":1794530417050},"kev":null,"epss":null,"p0":false},"mergedInto":null,"publisher":"Event Monitor Cyber"}