CVE-2024-1899Public exploitNetwork attack vector

Service interruption via nested anchor-parsing regex

Published Feb 26, 2024 · Updated Aug 1, 2024

Regular expression denial of service in Showdown 2.1.0 and earlier allows remote attackers to interrupt Markdown conversion via malicious links. The anchors subparser applies a nested regular expression to crafted sequences of unmatched opening brackets, causing excessive backtracking. Exposure requires a consuming application to pass attacker-controlled Markdown into Showdown; processing can tie up its worker without affecting data.

CVSS severity5.3
Medium
EPSS probability0.81%
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 Showdown 2.1.0 and earlier allows remote attackers to interrupt Markdown conversion via malicious links. The anchors subparser applies a nested regular expression to crafted sequences of unmatched opening brackets, causing excessive backtracking. Exposure requires a consuming application to pass attacker-controlled Markdown into Showdown; processing can tie up its worker without affecting data.

The record

CVE
CVE-2024-1899
Published
Feb 26, 2024
Updated
Aug 1, 2024
Vendor
ShowdownJS
Product
Showdown
Classifications
CWE-674, CWE-777, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 26, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 1, 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 <=2.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ShowdownJS · Showdownversion=0 <=2.1.0

Published CVSS scores

5.3TenableCVSS:3.1/AV:N/AC:L/PR:N/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-674Uncontrolled Recursion
CWE-777Regular Expression without Anchors
T1499.004Endpoint Denial of Service: Application 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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