CVE-2021-43843

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

2.0% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-12-20 22:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 04:11 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 2.0% in the next 30 days (EPSS).
• Severity: 5.3 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-12-20 22:15 UTC

Last modified

2026-06-17 04:11 UTC

Exploit probability

2.0% · EPSS, next 30 days

Weakness

CWE-400 · Uncontrolled resource consumption

Record status

Modified

Affected

• jsx-slack Project jsx-slack < 4.5.2

Attack profile CVSS 3.1 · 5.3

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-43843.md and follow it. Check whether this project is affected by CVE-2021-43843. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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