CVE-2021-4305Public exploitNetwork attack vector

Service interruption via repeated wildcard regex backtracking

Published Jan 5, 2023 · Updated Nov 25, 2024

Regular expression denial of service in robots-txt-guard before 1.0.2 allows remote attackers to hang consuming Node.js applications. makePathPattern turns runs of asterisks into repeated adjacent greedy wildcard groups, causing exponential backtracking during path matching. Impact requires a consuming application to build rules from attacker-controlled robots.txt patterns and match a crafted path.

CVSS severity7.5
High
EPSS probability0.95%
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 robots-txt-guard before 1.0.2 allows remote attackers to hang consuming Node.js applications. makePathPattern turns runs of asterisks into repeated adjacent greedy wildcard groups, causing exponential backtracking during path matching. Impact requires a consuming application to build rules from attacker-controlled robots.txt patterns and match a crafted path.

The record

CVE
CVE-2021-4305
Published
Jan 5, 2023
Updated
Nov 25, 2024
Vendor
WooRank
Product
robots-txt-guard
Classifications
CWE-1333, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 5, 2023CVE publishedPublication date reported by the CVE source.
  2. Nov 25, 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=n/a

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

WooRank · robots-txt-guardversion=n/a

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.5VulDBCVSS:3.1/AV:A/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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
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

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Your stack

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