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multiparty vulnerable to Denial of Service via Prototype Pollution leading to Uncaught Exception

High
UlisesGascon published GHSA-qxch-whhj-8956 May 12, 2026

Package

npm multiparty (npm)

Affected versions

<=4.2.3

Patched versions

>=4.3.0

Description

Impact

multiparty@4.2.3 and lower versions are vulnerable to denial of service via uncaught exception. By sending a multipart/form-data request with a field name that collides with an inherited Object.prototype property (e.g., __proto__, constructor, toString), the parser invokes .push() on the inherited prototype value rather than an array, throwing a TypeError that propagates as an uncaught exception and crashes the process. Any service accepting multipart uploads via multiparty is affected.

Patches

Users should upgrade to multiparty@4.3.0 or higher.

Workarounds

None.

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVE ID

CVE-2026-8161

Weaknesses

Uncaught Exception

An exception is thrown from a function, but it is not caught. Learn more on MITRE.

Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. Learn more on MITRE.

Credits