Prototype Pollution

published 2021-10-20 5 y ago modified 2026-06-17 4 mo ago also GHSA-4mvj-rq4v-2fxw , EUVD-2021-2155

cvss: 8.6; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 1.6%; EPSS 1.6% chance of exploitation in 30 days, percentile 75%
public exploits: 0; none known

This affects all versions of package x-assign. The global proto object can be polluted using the __proto__ object.

Exploit prediction

1.55% chance of exploitation in the next 30 days, higher than 75% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

snyk.io https://snyk.io/vuln/SNYK-JS-XASSIGN-1759314 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	8.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L/E:P
CNA	3.1	8.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L
NVD	3.1	9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD	2.0	7.5	AV:N/AC:L/Au:N/C:P/I:P/A:P
GitHub	3.1	8.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

Affected packages

ecosystem	package	affected	fixed in
npm	x-assign	<=0.1.4	no fix listed

Affected products

n/a x-assign

Classification

Weakness

CWE-1321 Improperly Controlled Modification of Object Prototype Attributes
CWE-915 Improperly Controlled Modification of Dynamically-Determined Object Attributes

References

snyk.io /vuln/SNYK-JS-XASSIGN-1759314
web, exploit, third-party-advisory
runkit.com /embed/sq8qjwemyn8t
web, third-party-advisory, url-repurposed
nvd.nist.gov /vuln/detail/CVE-2021-23452
advisory
github.com /mvoorberg/x-assign
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary