CVE-2021-43843: Insufficient patch for Regular Expression Denial of Service (ReDoS) to jsx-slack v4.5.1

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 2.0% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-12-20 · updated 2026-06-17
Weakness: CWE-400

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.

Affected products

yhatt jsx-slack: before 4.5.2 — fixed in 4.5.2

How to fix

Upgrade to a fixed version: yhatt jsx-slack 4.5.2. Check the vendor advisory for mitigations.

References

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