CVE-2021-3757Public exploitNetwork attack vector

Prototype pollution via array-typed patch path keys

Published Sep 2, 2021 · Updated Aug 3, 2024

Prototype pollution in Michel Weststrate Immer 9.0.5 and earlier allows attackers to modify inherited object properties through crafted patches. The applyPatches_ path check compares reserved names as strings, so array-wrapped proto or constructor keys evade strict equality and reach the object prototype. Exploitation requires attacker-controlled patch paths to reach applyPatches; polluted properties can alter application data or interrupt the consuming process.

CVSS severity9.8
Critical
EPSS probability1.65%
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 Michel Weststrate Immer 9.0.5 and earlier allows attackers to modify inherited object properties through crafted patches. The applyPatches_ path check compares reserved names as strings, so array-wrapped proto or constructor keys evade strict equality and reach the object prototype. Exploitation requires attacker-controlled patch paths to reach applyPatches; polluted properties can alter application data or interrupt the consuming process.

The record

CVE
CVE-2021-3757
Published
Sep 2, 2021
Updated
Aug 3, 2024
Vendor
Michel Weststrate
Product
Immer
Classifications
CWE-1321
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 2, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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 <=9.0.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Michel Weststrate · Immerversion=unspecified <=9.0.5

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5huntr.devCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

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-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Public exploit references

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Technologies

Your stack

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Your stack

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