CVE-2021-3807Public exploitNetwork attack vector

CPU exhaustion via nested regex repetitions

Published Sep 17, 2021 · Updated Aug 3, 2024

ReDoS in Chalk ansi-regex 3.0.0, 4.0.0 through 4.1.0, 5.0.0, and 6.0.0 allows attackers to exhaust CPU via crafted ANSI text. The exported ansiRegex pattern nests unbounded repetitions over semicolon-prefixed parameter text, causing excessive backtracking on invalid ANSI escape codes. Impact requires a consuming application to run the expression on attacker-controlled text, especially in a server context, and is limited to availability.

CVSS severity7.5
High
EPSS probability3.55%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

ReDoS in Chalk ansi-regex 3.0.0, 4.0.0 through 4.1.0, 5.0.0, and 6.0.0 allows attackers to exhaust CPU via crafted ANSI text. The exported ansiRegex pattern nests unbounded repetitions over semicolon-prefixed parameter text, causing excessive backtracking on invalid ANSI escape codes. Impact requires a consuming application to run the expression on attacker-controlled text, especially in a server context, and is limited to availability.

The record

CVE
CVE-2021-3807
Published
Sep 17, 2021
Updated
Aug 3, 2024
Vendor
Chalk
Product
ansi-regex
Classifications
CWE-1333, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 17, 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=unspecified <5.0.1
  2. Affected versionversion=unspecified <6.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Chalk · ansi-regexversion=unspecified <5.0.1; version=unspecified <6.0.1

Published CVSS scores

7.5GitHubCVSS: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-1333Inefficient Regular Expression Complexity
T1499.003Application Exhaustion Flood

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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