CVE-2021-43308Public exploitNetwork attack vector

Service interruption via exponential regex backtracking

Published Jun 1, 2022 · Updated Sep 16, 2024

Regular-expression denial of service in markdown-link-extractor before 3.0.2 and in 4.0.0 allows attackers to interrupt consuming services. The exported function processes a crafted image-link prefix and repeated escaped quotes with a link-extraction expression that enters exponential backtracking. Reachability requires a consuming application to pass arbitrary attacker input to the function, causing CPU exhaustion that blocks parsing and interrupts that application.

CVSS severity5.9
Medium
EPSS probability1.08%
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 markdown-link-extractor before 3.0.2 and in 4.0.0 allows attackers to interrupt consuming services. The exported function processes a crafted image-link prefix and repeated escaped quotes with a link-extraction expression that enters exponential backtracking. Reachability requires a consuming application to pass arbitrary attacker input to the function, causing CPU exhaustion that blocks parsing and interrupts that application.

The record

CVE
CVE-2021-43308
Published
Jun 1, 2022
Updated
Sep 16, 2024
Vendor
Thomas Cort
Product
markdown-link-extractor
Classifications
CWE-1333, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 1, 2022CVE 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=unspecified <3.0.2 changes=[{"at":"4.0.1","status":"unaffected"}]

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Thomas Cort · markdown-link-extractorversion=unspecified <3.0.2 changes=[{"at":"4.0.1","status":"unaffected"}]

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
5.9JFrogCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5NIST NVDCVSS: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
T1499.004Application 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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