CVE-2026-21452: MessagePack for Java denial of service via EXT32 payload length

Summary

MessagePack for Java versions prior to 0.9.11 are vulnerable to a denial-of-service flaw when deserializing .msgpack files containing EXT32 objects with attacker-controlled payload lengths. When ExtensionValue.getData() is invoked, the library allocates a byte array of the declared length without an upper bound, so a file only a few bytes long can exhaust the JVM heap, terminate the process, or make the service unavailable.

Mitigation

Fixed in 0.9.11.

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