CVE-2021-23436: Prototype Pollution

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.8% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-09-01 · updated 2026-06-17
Weakness: CWE-843

Description

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 type.

Affected products

immer: before 9.0.6 — fixed in 9.0.6

How to fix

Upgrade to a fixed version: immer 9.0.6. Check the vendor advisory for mitigations.

References

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