CVE-2021-23436: This affects the package immer before 9.0.6

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MEDIUM 5.6REMOTEUPGRADE

CVE-2021-23436 is a medium-severity flaw (CVSS 5.6) affecting immer. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

This affects the package immer before 9.0.6. A type confusion vulnerability can lead to a bypass of CVE-2020-28477 when the user-provided keys used in the path parameter are arrays. In particular, this bypass is possible because the condition (p === "__proto__" || p === "constructor") in applyPatches_ returns false if p is ['__proto__'] (or ['constructor']). The === operator (strict equality operator) returns false if the operands have different

Why this priority

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

A fixed release or distro patch exists.

Risk facts

CVSS score	5.6 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	1.8% (top 22%)
CISA exploited list	No
Weakness	CWE-843
Published	2021-09-01
Last modified	2026-06-17

Publisher (CNA): Snyk · 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

2021-09-01 18:15 UTCPublished CVE record published
2026-06-17 03:38 UTCUpdated Record last modified

immer project immer UPGRADE

Affected: < 9.0.6

Fixed in: 9.0.6

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls immer

2. UPGRADE to 9.0.6

npm install immer@">=9.0.6"

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-2021-23436?

immer: upgrade to 9.0.6. Exact commands for each OS are on this page.

Is CVE-2021-23436 being exploited?

CVE-2021-23436 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-2021-23436 affect?

CVE-2021-23436 affects immer. Severity is medium (CVSS 5.6). This affects the package immer before 9.0.6. A type confusion vulnerability can lead to a bypass of CVE-2020-28477 when the user-provided keys used in the path parameter are arrays. In particular, this bypass is possible because the conditi

How urgent is CVE-2021-23436?

Priority 49/100. Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2021-3757 CRITICAL 9.8 UPGRADE immer is vulnerable to Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution
CVE-2020-28477 HIGH 7.5 UPGRADE This affects all versions of package immer.

References

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