CVE-2021-40663Public exploitNetwork attack vector

Prototype pollution via unsafe deep merge

Published Jun 30, 2022 · Updated Aug 4, 2024

Prototype pollution in deep.assign 0.0.0-alpha.0 allows remote attackers to alter object prototypes via crafted input. The deepAssign function merges a JSON object containing a proto property into a target object without preventing prototype mutation. Exploitation requires an application to pass attacker-controlled data to this package; polluted prototypes can enable information disclosure, service interruption, or code execution depending on reachable application behavior.

CVSS severity9.8
Critical
EPSS probability1.79%
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 deep.assign 0.0.0-alpha.0 allows remote attackers to alter object prototypes via crafted input. The deepAssign function merges a JSON object containing a proto property into a target object without preventing prototype mutation. Exploitation requires an application to pass attacker-controlled data to this package; polluted prototypes can enable information disclosure, service interruption, or code execution depending on reachable application behavior.

The record

CVE
CVE-2021-40663
Published
Jun 30, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-1321
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 30, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NVDAV: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

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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