By exploiting an Open Redirect vulnerability on a website, an attacker could have spoofed the site displayed in the download file dialog to show the original site (the one suffering from the open redirect) rather than the site the file was actually downloaded from. This vulnerability affects Firefox < 81, Thunderbird < 78.3, and Firefox ESR < 78.3.
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00074.html
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00077.html
https://bugzilla.mozilla.org/show_bug.cgi?id=1641487
https://lists.debian.org/debian-lts-announce/2020/10/msg00020.html
https://security.gentoo.org/glsa/202010-02
https://www.debian.org/security/2020/dsa-4770
https://www.mozilla.org/security/advisories/mfsa2020-42/
Source: MITRE
Published: 2020-10-01
Updated: 2020-11-02
Type: CWE-601
Base Score: 5.8
Vector: AV:N/AC:M/Au:N/C:P/I:P/A:N
Impact Score: 4.9
Exploitability Score: 8.6
Severity: MEDIUM
Base Score: 6.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Impact Score: 2.7
Exploitability Score: 2.8
Severity: MEDIUM