CVE-2021-27405Public exploitNetwork attack vector

Service interruption via excessive regex backtracking

Published Feb 19, 2021 · Updated Aug 3, 2024

Regular expression denial of service in @progfay/scrapbox-parser before 6.0.3 and 7.0.0 through 7.0.1 allows attackers to exhaust CPU. The DecorationNode and StrongNode matchers apply ambiguous expressions to long runs of unmatched opening brackets, causing excessive backtracking. ExternalLinkNode has the same inefficient matching class, and applications that parse attacker-controlled bracket-heavy text can suffer CPU exhaustion and interruption.

CVSS severity4.3
Medium
EPSS probability1.76%
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 @progfay/scrapbox-parser before 6.0.3 and 7.0.0 through 7.0.1 allows attackers to exhaust CPU. The DecorationNode and StrongNode matchers apply ambiguous expressions to long runs of unmatched opening brackets, causing excessive backtracking. ExternalLinkNode has the same inefficient matching class, and applications that parse attacker-controlled bracket-heavy text can suffer CPU exhaustion and interruption.

The record

CVE
CVE-2021-27405
Published
Feb 19, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 19, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5GitLab Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.3GitHubCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

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-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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