msgpack-ruby JRuby decoder makes uncapped header-count allocations; a 5-byte message forces multi-GiB OOM

Summary The JRuby implementation of msgpack msgpack gem, java platform — pure Java decoder under ext/java/ sizes containers directly from the element count written in the message header, with no cap at all: no equivalent of the C unpacker's SHRTMAX clamp since 1.7.3 and none of the buffered-bytes...

CVE-2026-126366

The msgpack-ruby gem for the JRuby platform (versions prior to 1.8.7 ) is vulnerable to a memory exhaustion issue. The msgpack-java decoder incorrectly allocates arrays and byte buffers based on attacker-controlled sizes provided in array32 , str32 , and bin32 headers without verifying the availa...