CVE-2021-23424Public exploitNetwork attack vector

Service hang via nested regex quantifiers

Published Aug 18, 2021 · Updated Sep 16, 2024

Regular expression denial of service in Tjatse ansi-html before 0.0.8 allows attackers to hang Node.js processing via crafted ANSI text. The ansiHTML replacement regex repeats a digit group inside a Kleene star, causing exponential backtracking when an ESC-[ digit sequence lacks a terminating m. Any application that passes attacker-controlled text to the converter can pin a Node.js event-loop thread at full CPU, interrupting service.

CVSS severity7.5
High
EPSS probability1.98%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular expression denial of service in Tjatse ansi-html before 0.0.8 allows attackers to hang Node.js processing via crafted ANSI text. The ansiHTML replacement regex repeats a digit group inside a Kleene star, causing exponential backtracking when an ESC-[ digit sequence lacks a terminating m. Any application that passes attacker-controlled text to the converter can pin a Node.js event-loop thread at full CPU, interrupting service.

The record

CVE
CVE-2021-23424
Published
Aug 18, 2021
Updated
Sep 16, 2024
Vendor
Tjatse
Product
ansi-html
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 18, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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=0 <unspecified

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Tjatse · ansi-htmlversion=0 <unspecified

Published CVSS scores

7.5SnykCVSS:3.1/AV:N/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.

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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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.004Application or System Exploitation

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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