Origin Validation Error Affecting thunderbird package, versions <1:91.3.0-1

Note: Versions mentioned in the description apply only to the upstream thunderbird package and not the thunderbird package as distributed by Debian. See How to fix? for Debian:12 relevant fixed versions and status.

The Opportunistic Encryption feature of HTTP2 (RFC 8164) allows a connection to be transparently upgraded to TLS while retaining the visual properties of an HTTP connection, including being same-origin with unencrypted connections on port 80. However, if a second encrypted port on the same IP address (e.g. port 8443) did not opt-in to opportunistic encryption; a network attacker could forward a connection from the browser to port 443 to port 8443, causing the browser to treat the content of port 8443 as same-origin with HTTP. This was resolved by disabling the Opportunistic Encryption feature, which had low usage. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.

• https://security-tracker.debian.org/tracker/CVE-2021-38507
• https://bugzilla.mozilla.org/show_bug.cgi?id=1730935
• https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
• https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
• https://security.gentoo.org/glsa/202202-03
• https://security.gentoo.org/glsa/202208-14
• https://www.debian.org/security/2021/dsa-5026
• https://www.debian.org/security/2022/dsa-5034
• https://www.mozilla.org/security/advisories/mfsa2021-48/
• https://www.mozilla.org/security/advisories/mfsa2021-49/
• https://www.mozilla.org/security/advisories/mfsa2021-50/