CVE-2021-25916Public exploitNetwork attack vector

Service crash via Object.prototype pollution

Published Mar 16, 2021 · Updated Apr 30, 2025

Prototype pollution in Patchmerge 1.0.0 through 1.0.1 allows attackers to corrupt inherited object properties via crafted JSON merge patches. The objectMerge recursion follows a proto property into Object.prototype and writes attacker-controlled names and values there instead of creating an own object. An application must pass attacker-controlled patch data to the library; the resulting process-wide property changes crash the service or, when a suitable gadget exists, enable code execution.

CVSS severity9.8
Critical
EPSS probability3.51%
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 Patchmerge 1.0.0 through 1.0.1 allows attackers to corrupt inherited object properties via crafted JSON merge patches. The objectMerge recursion follows a proto property into Object.prototype and writes attacker-controlled names and values there instead of creating an own object. An application must pass attacker-controlled patch data to the library; the resulting process-wide property changes crash the service or, when a suitable gadget exists, enable code execution.

The record

CVE
CVE-2021-25916
Published
Mar 16, 2021
Updated
Apr 30, 2025
Vendor
Paul Humphreys
Product
Patchmerge
Classifications
CWE-1321
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 16, 2021CVE publishedPublication date reported by the CVE source.
  2. Apr 30, 2025Record 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=1.0.0, 1.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Paul Humphreys · Patchmergeversion=1.0.0, 1.0.1

Published CVSS scores

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8NIST NVDCVSS: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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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