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No exploitation reportedFix available

CVE-2021-43843

No exploitation reported by the sources we read.

  • Published2021-12-20
  • Fixed in4.5.2
  • WeaknessCWE-1333 · CWE-400

Am I affected?

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Description

jsx-slack is a package for building JSON objects for Slack block kit surfaces from JSX. The maintainers found the patch for CVE-2021-43838 in jsx-slack v4.5.1 is insufficient tfor protection from a Regular Expression Denial of Service (ReDoS) attack. If an attacker can put a lot of JSX elements into `<blockquote>` tag _with including multibyte characters_, an internal regular expression for escaping characters may consume an excessive amount of computing resources. v4.5.1 passes the test against ASCII characters but misses the case of multibyte characters. jsx-slack v4.5.2 has updated regular expressions for escaping blockquote characters to prevent catastrophic backtracking. It is also including an updated test case to confirm rendering multiple tags in `<blockquote>` with multibyte characters.

Timeline

dates in UTC
  1. 2021-12-2022:15CVE publishedNVD

Versions per branch

NVD · OSV
Jsx-slack project jsx-slack
BranchAffectedFixed in
4.5< 4.5.24.5.2

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

  1. Update Jsx-slack project jsx-slack to 4.5.2

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • CNACVSS 3.15.3known since 2026-10-23
  • NVDCVSS 3.17.5read 2026-10-23
  • NVDCVSS 2.05read 2026-10-23
  • CNAweakness (CWE)CWE-1333, CWE-400known since 2026-10-23
  • FIRST EPSSEPSS score2.0 %2026-11-09
  • OSVaffected packages—
  • GitHub AdvisoriesadvisoryMODERATE2022-01-04

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2021-12-20
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-hp68-xhvj-x6j6

Frequently asked questions

What is CVE-2021-43843?

jsx-slack is a package for building JSON objects for Slack block kit surfaces from JSX. The maintainers found the patch for CVE-2021-43838 in jsx-slack v4.5.1 is insufficient tfor protection from a Regular Expression Denial of Service (ReDoS) attack. If an attacker can put a lot of JSX elements into `<blockquote>` tag _with including multibyte characters_, an internal regular expression for escaping characters may consume an excessive amount of computing resources. v4.5.1 passes the test against ASCII characters but misses the case of multibyte characters. jsx-slack v4.5.2 has updated regular expressions for escaping blockquote characters to prevent catastrophic backtracking. It is also including an updated test case to confirm rendering multiple tags in `<blockquote>` with multibyte characters.

Is CVE-2021-43843 actively exploited?

Active exploitation of CVE-2021-43843 has not been confirmed. Its EPSS score was 2.0% on 2026-11-09, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-43843?

CVE-2021-43843 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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