CVE-2021-4279Public exploitNetwork attack vector

Object prototype modification via constructor/prototype paths

Published Dec 25, 2022 · Updated Aug 3, 2024

Prototype pollution in Starcounter-Jack JSON-Patch before 3.1.1 allows remote attackers to alter inherited object properties via crafted patches. The applyOperation function blocked proto path segments but followed constructor/prototype segments, letting a replace operation write to the shared object prototype. Exploitation requires a consuming application to pass attacker-controlled patch operations to the library; polluted inherited properties can corrupt application behavior, while further impact depends on that application.

CVSS severity9.8
Critical
EPSS probability1.08%
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 Starcounter-Jack JSON-Patch before 3.1.1 allows remote attackers to alter inherited object properties via crafted patches. The applyOperation function blocked proto path segments but followed constructor/prototype segments, letting a replace operation write to the shared object prototype. Exploitation requires a consuming application to pass attacker-controlled patch operations to the library; polluted inherited properties can corrupt application behavior, while further impact depends on that application.

The record

CVE
CVE-2021-4279
Published
Dec 25, 2022
Updated
Aug 3, 2024
Vendor
Starcounter-Jack
Product
JSON-Patch
Classifications
CWE-1321
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 25, 2022CVE 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=3.0
  2. Affected versionversion=3.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Starcounter-Jack · JSON-Patchversion=3.0; version=3.1

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
6.3VulDBCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
7.3GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

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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