msgpack MessagePack for Ruby up to 1.8.6 Unpacker MessagePack.unpack array32/str32/bin32 allocation of resources

Summaryinfo

A vulnerability has been found in msgpack MessagePack for Ruby up to 1.8.6 and classified as problematic. Affected by this vulnerability is the function MessagePack.unpack of the component Unpacker. This manipulation of the argument array32/str32/bin32 causes allocation of resources. The identification of this vulnerability is CVE-2026-126366. It is possible to initiate the attack remotely. There is no exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in msgpack MessagePack for Ruby up to 1.8.6. It has been declared as problematic. Affected by this vulnerability is the function MessagePack.unpack of the component Unpacker. The manipulation of the argument array32/str32/bin32 with an unknown input leads to a allocation of resources vulnerability. The CWE definition for the vulnerability is CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. As an impact it is known to affect availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-126366 since 11/10/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 1.8.7 eliminates this vulnerability.

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Productinfo

Type

• Ruby Gem

Vendor

• msgpack

Name

• MessagePack for Ruby

Version

• 1.8.0
• 1.8.1
• 1.8.2
• 1.8.3
• 1.8.4
• 1.8.5
• 1.8.6

CPE 2.3info

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CPE 2.2info

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