CVE-2021-23436Public exploitNetwork attack vector

Prototype pollution via array-wrapped patch keys

Published Sep 1, 2021 · Updated Sep 16, 2024

Prototype pollution in Immer 7.0.0 through 9.0.5 allows remote attackers to modify Object.prototype via crafted patch paths. applyPatches_ compares each path element directly with reserved strings, so an array-wrapped proto key evades the check and is used for property traversal. Exploitation requires an application to pass attacker-controlled patch paths to applyPatches_; polluted properties can alter behavior across objects in that JavaScript process.

CVSS severity9.8
Critical
EPSS probability1.78%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Prototype pollution in Immer 7.0.0 through 9.0.5 allows remote attackers to modify Object.prototype via crafted patch paths. applyPatches_ compares each path element directly with reserved strings, so an array-wrapped proto key evades the check and is used for property traversal. Exploitation requires an application to pass attacker-controlled patch paths to applyPatches_; polluted properties can alter behavior across objects in that JavaScript process.

The record

CVE
CVE-2021-23436
Published
Sep 1, 2021
Updated
Sep 16, 2024
Vendor
Michel Weststrate
Product
Immer
Classifications
CWE-843, CWE-1321
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 1, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <9.0.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Michel Weststrate · Immerversion=unspecified <9.0.6

Published CVSS scores

9.8GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-843Access of Resource Using Incompatible Type ('Type Confusion')
CWE-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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