msgpack5 is a msgpack v5 implementation for node.js and the browser. In msgpack5 before versions 3.6.1, 4.5.1, and 5.2.1 there is a "Prototype Poisoning" vulnerability. When msgpack5 decodes a map containing a key "__proto__", it assigns the decoded value to __proto__. Object.prototype.__proto__ is an accessor property for the receiver's prototype. If the value corresponding to the key __proto__ decodes to an object or null, msgpack5 sets the decoded object's prototype to that value. An attacker who can submit crafted MessagePack data to a service can use this to produce values that appear to be of other types; may have unexpected prototype properties and methods (for example length, numeric properties, and push et al if __proto__'s value decodes to an Array); and/or may throw unexpected exceptions when used (for example if the __proto__ value decodes to a Map or Date). Other unexpected behavior might be produced for other types. There is no effect on the global prototype. This "prototype poisoning" is sort of a very limited inversion of a prototype pollution attack. Only the decoded value's prototype is affected, and it can only be set to msgpack5 values (though if the victim makes use of custom codecs, anything could be a msgpack5 value). We have not found a way to escalate this to true prototype pollution (absent other bugs in the consumer's code). This has been fixed in msgpack5 version 3.6.1, 4.5.1, and 5.2.1. See the referenced GitHub Security Advisory for an example and more details.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - msgpack5 is a msgpack v5 implementation for node.js and the browser. In msgpack5 before versions 3.6.1,
    4.5.1, and 5.2.1 there is a "Prototype Poisoning" vulnerability. When msgpack5 decodes a map containing a
    key "__proto__", it assigns the decoded value to __proto__. Object.prototype.__proto__ is an accessor
    property for the receiver's prototype. If the value corresponding to the key __proto__ decodes to an
    object or null, msgpack5 sets the decoded object's prototype to that value. An attacker who can submit
    crafted MessagePack data to a service can use this to produce values that appear to be of other types; may
    have unexpected prototype properties and methods (for example length, numeric properties, and push et al
    if __proto__'s value decodes to an Array); and/or may throw unexpected exceptions when used (for example
    if the __proto__ value decodes to a Map or Date). Other unexpected behavior might be produced for other
    types. There is no effect on the global prototype. This "prototype poisoning" is sort of a very limited
    inversion of a prototype pollution attack. Only the decoded value's prototype is affected, and it can only
    be set to msgpack5 values (though if the victim makes use of custom codecs, anything could be a msgpack5
    value). We have not found a way to escalate this to true prototype pollution (absent other bugs in the
    consumer's code). This has been fixed in msgpack5 version 3.6.1, 4.5.1, and 5.2.1. See the referenced
    GitHub Security Advisory for an example and more details. (CVE-2021-21368)

ID	Name	Product	Family	Severity
415208	SCA: security update for msgpack5 (GHSA-gmjw-49p4-pcfm)	Tenable Cloud Security	SCA Checks	high
415208	SCA: security update for msgpack5 (GHSA-gmjw-49p4-pcfm)	Tenable Self-Hosted Container Security	SCA Checks	high

Detections

Analytics

CVE-2021-21368

high

Tenable Plugins

high

high