CVE-2018-16489: A prototype pollution vulnerability was found in just-extend <4.0.0 that allows attack to inject properties on

Q: How urgent is CVE-2018-16489?

Priority 64/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2018-16489 is a critical-severity flaw (CVSS 9.8) affecting just-extend. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.8% (top 21%)
CISA exploited list	No
Weakness	CWE-400, CWE-74
Published	2019-02-01
Last modified	2026-06-17

Publisher (CNA): HackerOne · Vendor: just-extend project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2019-02-01 18:29 UTCPublished CVE record published
2026-06-17 01:44 UTCUpdated Record last modified

just-extend project just-extend UPGRADE

Affected: < 4.0.0

Fixed in: 4.0.0

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls just-extend

2. UPGRADE to 4.0.0

npm install just-extend@">=4.0.0"

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2018-16489?

just-extend: upgrade to 4.0.0. Exact commands for each OS are on this page.

Is CVE-2018-16489 being exploited?

CVE-2018-16489 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2018-16489 affect?

CVE-2018-16489 affects just-extend. Severity is critical (CVSS 9.8). A prototype pollution vulnerability was found in just-extend <4.0.0 that allows attack to inject properties onto Object.prototype through its functions.

How urgent is CVE-2018-16489?

Priority 64/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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