Through complicated navigations with new windows, an HTTP page could have inherited a secure lock icon from an HTTPS page. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-23998
• https://bugzilla.mozilla.org/show_bug.cgi?id=1667456
• https://www.mozilla.org/security/advisories/mfsa2021-14/
• https://www.mozilla.org/security/advisories/mfsa2021-15/
• https://www.mozilla.org/security/advisories/mfsa2021-16/