What’s Vulnerable › Vulnerabilities

CVE-2021-43838: Regular Expression Denial of Service (ReDoS) in jsx-slack

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.4% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-12-17 · updated 2026-06-17
• Weakness: CWE-400

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.

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

• https://github.com/yhatt/jsx-slack/commit/36e4a10405e4c7745333e245fcc5029c02c7065d
• https://github.com/yhatt/jsx-slack/security/advisories/GHSA-55xv-f85c-248q
• https://github.com/yhatt/jsx-slack/commit/36e4a10405e4c7745333e245fcc5029c02c7065d
• https://github.com/yhatt/jsx-slack/security/advisories/GHSA-55xv-f85c-248q

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