CVE-2024-34078: Arbitrary HTML present after sanitization because of unicode normalization

May 6, 2024

If using keep_typographic_whitespace=False (which is the default), the sanitizer normalizes unicode to the NFKC form at the end. Some unicode characters normalize to chevrons; this allows specially crafted HTML to escape sanitization.

References

github.com/advisories/GHSA-wvhx-q427-fgh3
github.com/matthiask/html-sanitizer
github.com/matthiask/html-sanitizer/commit/48db42fc5143d0140c32d929c46b802f96913550
github.com/matthiask/html-sanitizer/security/advisories/GHSA-wvhx-q427-fgh3
nvd.nist.gov/vuln/detail/CVE-2024-34078

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