jsx-slack insufficient patch for CVE-2021-43838 ReDoS

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

• CVE-2021-43843: 1.98% estimated exploitation activity in the next 30 days; percentile 80.56 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

We found the patch for CVE-2021-43838 in jsx-slack v4.5.1 is insufficient to save from Regular Expression Denial of Service (ReDoS) attack. This vulnerability affects to jsx-slack v4.5.1 and earlier versions. Impact If 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 has released by passing the test against ASCII characters but missed the case of multibyte characters. https://github.com/yhatt/jsx-slack/security/advisories/GHSA-55xv-f85c-248q Patches 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. References - https://github.com/yhatt/jsx-slack/commit/46bc88391d89d5fda4ce689e18ca080bcdd29ecc Credits Thanks to @hieki for finding out…

Published by the source

6 Jan 2022, 18:34 UTC

Last modified by the source

4 Feb 2026, 02:28 UTC

Source last checked

26 Oct 2026, 12:17 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-hp68-xhvj-x6j6

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-hp68-xhvj-x6j6

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# Patch Next advisory brief: CVE-2021-43843

Advisory: jsx-slack insufficient patch for CVE-2021-43838 ReDoS
IDs: CVE-2021-43843, GHSA-hp68-xhvj-x6j6
Record: https://patchnext.com/advisories/cve-2021-43843 (revision 2, source checked 26 Oct 2026, 12:17 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: jsx-slack 4.5.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm jsx-slack: affected < 4.5.2; fixed in 4.5.2

## Suggested inspection (read-only)
- `npm ls jsx-slack --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on jsx-slack.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-hp68-xhvj-x6j6 (OSV record GHSA-hp68-xhvj-x6j6 lists affected ranges: npm jsx-slack >=0 <4.5.2 (fixed))
- Verified: https://github.com/advisories/GHSA-hp68-xhvj-x6j6 (GitHub-reviewed advisory GHSA-hp68-xhvj-x6j6 lists affected ranges: npm jsx-slack >=0 <4.5.2)

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