CVE-2021-26707Public exploitNetwork attack vector

Application property manipulation via constructor payload

Published Jun 2, 2021 · Updated Aug 3, 2024

Prototype pollution in merge-deep before 3.0.3 allows attackers to modify inherited application properties via crafted objects. The recursive merge accepts a constructor key and descends into its prototype member, allowing attacker-controlled values to mutate Object.prototype even though proto is blocked. A consuming application must pass attacker-influenced objects to the library; effects depend on how inherited properties are used and range from authorization changes or service crashes to code execution.

CVSS severity9.8
Critical
EPSS probability1.90%
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 merge-deep before 3.0.3 allows attackers to modify inherited application properties via crafted objects. The recursive merge accepts a constructor key and descends into its prototype member, allowing attacker-controlled values to mutate Object.prototype even though proto is blocked. A consuming application must pass attacker-influenced objects to the library; effects depend on how inherited properties are used and range from authorization changes or service crashes to code execution.

The record

CVE
CVE-2021-26707
Published
Jun 2, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-1321
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 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?

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

9.8GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
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 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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