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.

/** @jsxImportSource jsx-slack */
import { Section } from 'jsx-slack'

console.log(
  <Section>
    <blockquote>
      {[...Array(40)].map(() => (
        <p>亜</p>
      ))}
    </blockquote>
  </Section>
)

v4.5.1 has released by passing the test against ASCII characters but missed the case of multibyte characters.
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

• 46bc883

Credits

Thanks to @hieki for finding out this vulnerability.