CVE-2026-126366

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 above 2^31 did not use the affected allocation behavior. This issue is fixed in version 1.8.7.

• CWE-770
• CWE-1325

• https://github.com/msgpack/msgpack-ruby/commit/ca0efc1256c687b428c46dd68ce000ff515d53f2
• https://github.com/msgpack/msgpack-ruby/releases/tag/v1.8.6
• https://github.com/msgpack/msgpack-ruby/releases/tag/v1.8.7
• https://github.com/msgpack/msgpack-ruby/security/advisories/GHSA-73v3-wf97-vpgj

Published

Nov 13, 2026

Last Modified

Nov 13, 2026

Status

Received

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