CVE-2020-36632Public exploitNetwork attack vector

Prototype pollution via unfiltered __proto__ path segment

Published Dec 25, 2022 · Updated Aug 4, 2024

Prototype pollution in flat 5.0.0 allows remote attackers to alter inherited JavaScript object properties through crafted input. The unflatten function treats proto as an ordinary dotted-key segment and writes the supplied value into Object.prototype. Reachability requires an application to pass attacker-controlled keys to unflatten; corrupted inherited properties can alter application logic, while further impact depends on available property-use gadgets.

CVSS severity9.8
Critical
EPSS probability1.12%
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 flat 5.0.0 allows remote attackers to alter inherited JavaScript object properties through crafted input. The unflatten function treats proto as an ordinary dotted-key segment and writes the supplied value into Object.prototype. Reachability requires an application to pass attacker-controlled keys to unflatten; corrupted inherited properties can alter application logic, while further impact depends on available property-use gadgets.

The record

CVE
CVE-2020-36632
Published
Dec 25, 2022
Updated
Aug 4, 2024
Vendor
Hugh Kennedy
Product
flat
Classifications
CWE-1321
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Dec 25, 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?

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  1. Affected versionversion=5.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesUnavailable in this record.

What is affected?

Hugh Kennedy · flatversion=5.0

Published CVSS scores

6.3VulDBCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
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
PrivilegesUnavailable
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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