CVE-2021-43843: Jsx-Slack Project Jsx-Slack

High severity, CVSS 7.5. EPSS: 1.9% chance of exploitation in the next 30 days.

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.

Affected products

• Jsx-Slack Project Jsx-Slack: before 4.5.2 (fixed in 4.5.2)

Published 2021-12-20. Last modified 2026-06-17.