CVE-2021-38507 Information

Description

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.

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

Reference

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

Attack Complexity

LOW

Privileges Required

NONE

User Interaction Required

NONE

Scope

REQUIRED

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

HIGH

Base Score

NONE

Base Severity

6.5