CVE-2026-107353: traverse: set() can write to built-in prototypes via an untrusted path

Vulnerability summary

CVE-2026-107353 is a medium (CVSS 6.9) Prototype Pollution vulnerability in ljharb traverse. EPSS estimates a 0.28% chance of exploitation in the next 30 days, higher than 19.3% of scored vulnerabilities.

Timeline

1. 07-10-2026
   PublishedVulnerability first disclosed.
2. 07-10-2026
   Last modifiedVulnerability information updated.

Description

traverse (npm) versions 0.3.6 through 0.3.9, 0.4.0 through 0.4.6, 0.5.0 through 0.5.2, and 0.6.0 through 0.6.11 allow prototype pollution through set(). When the path passed to set() crosses a primitive value, the next path segment is resolved on that primitive's built-in prototype, so an application that passes an untrusted path to set() lets an attacker add or overwrite properties of String.prototype, Number.prototype, or Boolean.prototype using plain JSON data, for example traverse({ name: 'bob' }).set(['name', '__proto__', 'polluted'], 'yes'). Object.prototype was reachable only with a non-data path segment, such as an object whose toString returns a different value on each call, or through a Proxy that accepts an assignment without storing it. This is fixed in 0.3.10, 0.4.7, 0.5.3, and 0.6.12.

• CWE-1321Improperly 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.