If Firefox is installed to a user-writable directory, the Mozilla Maintenance Service would execute updater.exe from the install location with system privileges. Although the Mozilla Maintenance Service does ensure that updater.exe is signed by Mozilla, the version could have been rolled back to a previous version which would have allowed exploitation of an older bug and arbitrary code execution with System Privileges. Note: This issue only affected Windows operating systems. Other operating systems are unaffected.. This vulnerability affects Firefox < 80, Thunderbird < 78.2, Thunderbird < 68.12, Firefox ESR < 68.12, and Firefox ESR < 78.2.

References

• https://nvd.nist.gov/vuln/detail/CVE-2020-15663
• https://bugzilla.mozilla.org/show_bug.cgi?id=1643199
• https://www.mozilla.org/security/advisories/mfsa2020-36
• https://www.mozilla.org/security/advisories/mfsa2020-37
• https://www.mozilla.org/security/advisories/mfsa2020-38
• https://www.mozilla.org/security/advisories/mfsa2020-40
• https://www.mozilla.org/security/advisories/mfsa2020-41