CVE-2021-20088Public exploitNetwork attack vector

Object prototype modification via unsafe query parsing

Published Apr 23, 2021 · Updated Aug 3, 2024

Prototype pollution in MooTools More 1.6.0 allows remote authenticated users to modify Object.prototype through a crafted query string. String.parseQueryString traverses decoded bracketed keys and assigns obj[key] without blocking proto or constructor.prototype. A web application must pass attacker-controlled URL query data to the method; polluted inherited properties can alter downstream application behavior.

CVSS severity8.8
High
EPSS probability1.45%
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 MooTools More 1.6.0 allows remote authenticated users to modify Object.prototype through a crafted query string. String.parseQueryString traverses decoded bracketed keys and assigns obj[key] without blocking proto or constructor.prototype. A web application must pass attacker-controlled URL query data to the method; polluted inherited properties can alter downstream application behavior.

The record

CVE
CVE-2021-20088
Published
Apr 23, 2021
Updated
Aug 3, 2024
Vendor
MooTools
Product
MooTools More
Classifications
CWE-1321, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 23, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

MooTools · MooTools Moreversion=1.6.0

Published CVSS scores

8.8GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:L/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.

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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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
T1203Exploitation for Client Execution

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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