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[ CVE-2026-107299 · Published 8 Oct 2026 ]

msgpack5: Reserved byte can cause unbounded stream buffering

CVSS 5.9 EPSS <1%Fix available

[ Description ]Official description

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder treats the reserved MessagePack byte 0xc1 as incomplete input instead of invalid input. When 0xc1 begins a stream, subsequent data remains buffered while the decoder waits for bytes that cannot make the value valid, allowing a remote peer to exhaust memory. This issue is fixed in version 6.1.0.

[ Fixes ]Fixes and patches

  • msgpack5 6.1.0Fixed version · GitHub Advisories · npm package msgpack5: upgrade to 6.1.0 or later (affected < 6.1.0)

[ Packages ]Affected open-source packages

[ References ]References