CVE-2026-107301

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, constructing msgpack5 with an empty or partial options object disables the default protoAction: 'error' protection. A decoded map containing a proto key can then replace the decoded object's prototype, potentially changing inherited properties or downstream behavior, although Object.prototype is not modified globally. This issue is fixed in version 6.1.0.

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, constructing msgpack5 with an empty or partial options object disables the default protoAction: 'error' protection. A decoded map containing a proto key can then replace the decoded object's prototype, potentially changing inherited properties or downstream behavior, although Object.prototype is not modified globally. This issue is fixed in version 6.1.0.

Impact

Passing an empty or partial options object disables the default protoAction: 'error' protection. A map containing a __proto__ key can then replace the prototype of the decoded object, potentially changing inherited properties or causing unexpected behavior in downstream code.

Only the decoded object's prototype is affected; this does not modify Object.prototype globally.

Patches

Options are now merged with secure defaults without modifying the caller's object. Unsupported protoAction values are rejected.

Workarounds

Explicitly set protoAction: 'error' whenever constructing a msgpack5 instance, and validate decoded values before use.

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, constructing msgpack5 with an empty or partial options object disables the default protoAction: 'error' protection. A decoded map containing a proto key can then replace the decoded object's prototype, potentially changing inherited properties or downstream behavior, although Object.prototype is not modified globally. This issue is fixed in version 6.1.0.

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, constructing msgpack5 with an empty or partial options object disables the default protoAction: 'error' protection. A decoded map containing a proto key can then replace the decoded object's prototype, potentially changing inherited properties or downstream behavior, although Object.prototype is not modified globally. This issue is fixed in version 6.1.0.

Impact

Passing an empty or partial options object disables the default protoAction: 'error' protection. A map containing a __proto__ key can then replace the prototype of the decoded object, potentially changing inherited properties or causing unexpected behavior in downstream code.

Only the decoded object's prototype is affected; this does not modify Object.prototype globally.

Patches

Options are now merged with secure defaults without modifying the caller's object. Unsupported protoAction values are rejected.

Workarounds

Explicitly set protoAction: 'error' whenever constructing a msgpack5 instance, and validate decoded values before use.

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, constructing msgpack5 with an empty or partial options object disables the default protoAction: 'error' protection. A decoded map containing a proto key can then replace the decoded object's prototype, potentially changing inherited properties or downstream behavior, although Object.prototype is not modified globally. This issue is fixed in version 6.1.0.

TuxCare rebuilt msgpack5 to address 7 CVEs. Fixed in 3.6.1-tuxcare.1.