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High severity7.5GHSA Advisory· Published Jun 10, 2026· Updated Sep 9, 2026

CVE-2026-46625

CVE-2026-46625

Description

JavaScript Cookie is a JavaScript API for handling cookies, client-side. Prior to version 3.0.7, js-cookie's internal assign() helper copies properties with for...in + plain assignment. When the source object is produced by JSON.parse, the JSON object's "__proto__" member is an own enumerable property, so the for…in enumerates it and the target[key] = source[key] write triggers the Object.prototype.__proto__ setter on the fresh target ({}). The result is a per-instance prototype hijack: Object.prototype itself is untouched, but the merged attributes object now inherits attacker-controlled keys. Because the consuming set() function then enumerates the merged object with another for...in, every key the attacker placed on the polluted prototype lands in the resulting Set-Cookie string as an attribute pair. The attacker can set domain=, secure=, samesite=, expires=, and path= on cookies whose attributes the developer thought were locked down. This issue has been patched in version 3.0.7.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
js-cookienpm
< 3.0.73.0.7

Affected products

34

Patches

Vulnerability mechanics

References

18

News mentions

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