Due to unexpected data type conversions, a use-after-free could have occurred when interacting with the font cache. We presume that with enough effort this could have been exploited to run arbitrary code. This vulnerability affects Firefox < 88.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-23997
• https://bugzilla.mozilla.org/show_bug.cgi?id=1701942
• https://www.mozilla.org/security/advisories/mfsa2021-16/