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No exploitation reportedFix available

CVE-2021-43838

No exploitation reported by the sources we read.

  • Published2021-12-17
  • Fixed in4.5.1
  • WeaknessCWE-1333 · CWE-400

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into `<blockquote>` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.

Timeline

dates in UTC
  1. 2021-12-1719:15CVE publishedNVD

Versions per branch

OSV · NVD
jsx-slack
BranchAffectedFixed in
4.5< 4.5.14.5.1
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 to 4.5.1

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-400known since 2026-10-23
  • NVDweakness (CWE)CWE-1333read 2026-10-23
  • FIRST EPSSEPSS score1.4 %2026-11-09
  • OSVaffected packages—
  • GitHub AdvisoriesadvisoryLOW2021-12-17

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
2021-12-17
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-55xv-f85c-248q

Frequently asked questions

What is CVE-2021-43838?

jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into `<blockquote>` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.

Is CVE-2021-43838 actively exploited?

Active exploitation of CVE-2021-43838 has not been confirmed. Its EPSS score was 1.4% on 2026-11-09, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-43838?

CVE-2021-43838 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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