CVE-2021-32821Public exploitNetwork attack vector

Service interruption via exponential selector-parser backtracking

Published Jan 3, 2023 · Updated Mar 10, 2025

ReDoS in MooTools Core 1.6.0 and earlier allows attackers to interrupt applications via crafted CSS selector strings. Slick.parse in Source/Slick/Slick.Parser.js applies an ambiguous regular expression to the selector, causing exponential backtracking. Exploitation requires attacker-controlled selector input to reach the parser and can monopolize the executing JavaScript thread.

CVSS severity7.5
High
EPSS probability0.64%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

ReDoS in MooTools Core 1.6.0 and earlier allows attackers to interrupt applications via crafted CSS selector strings. Slick.parse in Source/Slick/Slick.Parser.js applies an ambiguous regular expression to the selector, causing exponential backtracking. Exploitation requires attacker-controlled selector input to reach the parser and can monopolize the executing JavaScript thread.

The record

CVE
CVE-2021-32821
Published
Jan 3, 2023
Updated
Mar 10, 2025
Vendor
MooTools
Product
MooTools Core
Classifications
CWE-400, CWE-1333, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 3, 2023CVE publishedPublication date reported by the CVE source.
  2. Mar 10, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=1.6.0 <=1.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

MooTools · MooTools Coreversion=1.6.0 <=1.6.0

Published CVSS scores

7.5GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
6.2UbuntuCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/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-400Uncontrolled Resource Consumption
CWE-1333Inefficient Regular Expression Complexity
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo