CVE-2021-25927Public exploitNetwork attack vector

Denial of service via unsafe unflatten paths

Published Apr 26, 2021 · Updated Apr 30, 2025

Prototype pollution in Jessie Barnett safe-flat 2.0.0 through 2.0.1 allows attackers to interrupt services via crafted object keys. The unflatten function splits attacker-controlled keys into path segments and follows proto, constructor, or prototype properties while building the result object. Exploitation requires a consuming application to pass attacker-controlled keys to unflatten; pollution can crash its process, while code execution depends on a separate application gadget.

CVSS severity9.8
Critical
EPSS probability3.34%
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 Jessie Barnett safe-flat 2.0.0 through 2.0.1 allows attackers to interrupt services via crafted object keys. The unflatten function splits attacker-controlled keys into path segments and follows proto, constructor, or prototype properties while building the result object. Exploitation requires a consuming application to pass attacker-controlled keys to unflatten; pollution can crash its process, while code execution depends on a separate application gadget.

The record

CVE
CVE-2021-25927
Published
Apr 26, 2021
Updated
Apr 30, 2025
Vendor
Jessie Barnett
Product
safe-flat
Classifications
CWE-1321
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 26, 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=2.0.0, 2.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Jessie Barnett · safe-flatversion=2.0.0, 2.0.1

Published CVSS scores

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

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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