Prototype Pollution in just-extend

published 2019-02-01 7 y ago modified 2026-06-17 4 mo ago also GHSA-675m-85rw-j3w4 , EUVD-2019-0238

cvss: 9.8; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.8%; EPSS 1.8% chance of exploitation in 30 days, percentile 79%
public exploits: 0; none known

A prototype pollution vulnerability was found in just-extend <4.0.0 that allows attack to inject properties onto Object.prototype through its functions.

Patch / fix

fixed in 2

npm just-extend 4.0.0
just-extend_project just-extend 4.0.0

Exploit prediction

1.84% chance of exploitation in the next 30 days, higher than 79% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

hackerone.com https://hackerone.com/reports/430291 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
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	9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem	package	affected	fixed in
npm	just-extend	<4.0.0	4.0.0

Affected products

HackerOne just-extend

Classification

Weakness

CWE-400 Uncontrolled Resource Consumption
CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component
CWE-1321 Improperly Controlled Modification of Object Prototype Attributes

References

hackerone.com /reports/430291
web, exploit, issue-tracking, third-party-advisory
nvd.nist.gov /vuln/detail/CVE-2018-16489
advisory
github.com /advisories/GHSA-675m-85rw-j3w4
advisory
npmjs.com /advisories/780
web

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