CVEvulnerability

CVE-2021-38507

6.5 MEDIUM Published 2021-12-08 Modified 2026-06-17 Official page ↗
Status
Modified
Published
2021-12-08
Last modified
2026-06-17
Assigner
[email protected]
CVSS 3.1 ([email protected])
6.5 MEDIUM — CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
CVSS 2.0 ([email protected])
4.3 MEDIUM — AV:N/AC:M/Au:N/C:N/I:P/A:N
Weaknesses
CWE-346

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.

Affected configurations

• mozilla firefox (< 94.0) • mozilla firefox esr (< 91.3.0) • mozilla thunderbird (< 91.3.0) • debian debian linux 9.0 • debian debian linux 10.0 • debian debian linux 11.0

Related

Weakness · CWE (1)

  • CWE-346 Origin Validation Error weakness

References