CVE-2021-43838Public exploitNetwork attack vector

Service interruption via catastrophic blockquote backtracking

Published Dec 17, 2021 · Updated Aug 4, 2024

ReDoS in jsx-slack 4.5.1 and earlier allows remote attackers to interrupt applications through JSX containing many blockquote elements. The blockquote escape expression catastrophically backtracks across tag sequences, while multibyte text bypasses the 4.5.1 workaround. Only applications that pass attacker-controlled JSX containing many blockquote elements to the library expose the CPU-exhaustion path.

CVSS severity5.3
Medium
EPSS probability1.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

ReDoS in jsx-slack 4.5.1 and earlier allows remote attackers to interrupt applications through JSX containing many blockquote elements. The blockquote escape expression catastrophically backtracks across tag sequences, while multibyte text bypasses the 4.5.1 workaround. Only applications that pass attacker-controlled JSX containing many blockquote elements to the library expose the CPU-exhaustion path.

The record

CVE
CVE-2021-43838
Published
Dec 17, 2021
Updated
Aug 4, 2024
Vendor
Yuki Hattori
Product
jsx-slack
Classifications
CWE-400, CWE-1333, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 17, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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=< 4.5.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Yuki Hattori · jsx-slackversion=< 4.5.1

Published CVSS scores

5.3GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
3.7OSVCVSS:3.1/AV:N/AC:H/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-400Uncontrolled Resource Consumption
CWE-1333Inefficient Regular Expression Complexity
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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