CVE-2021-3757: immer is vulnerable to Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2021-3757 is a critical-severity flaw (CVSS 9.8) affecting immer. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

immer is vulnerable to Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

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	1.7% (top 23%)
CISA exploited list	No
Weakness	CWE-1321
Published	2021-09-02
Last modified	2026-06-17

Publisher (CNA): huntr.dev · Vendor: immer project

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

Am I affected?

Timeline

2021-09-02 12:15 UTCPublished CVE record published
2026-06-17 04:05 UTCUpdated Record last modified

immer project immer UPGRADE

Affected: <= 9.0.5

Fixed in: newer than 9.0.5

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls immer

2. UPGRADE to newer than 9.0.5

npm install immer@">9.0.5"

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-2021-3757?

immer: upgrade to newer than 9.0.5. Exact commands for each OS are on this page.

Is CVE-2021-3757 being exploited?

CVE-2021-3757 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-2021-3757 affect?

CVE-2021-3757 affects immer. Severity is critical (CVSS 9.8). immer is vulnerable to Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

How urgent is CVE-2021-3757?

Priority 63/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2021-23436 MEDIUM 5.6 UPGRADE This affects the package immer before 9.0.6
CVE-2020-28477 HIGH 7.5 UPGRADE This affects all versions of package immer.

References

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