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.
Advisories
Source ID Title
Debian DLA Debian DLA DLA-2863-1 firefox-esr security update
Debian DLA Debian DLA DLA-2874-1 thunderbird security update
Debian DSA Debian DSA DSA-5026-1 firefox-esr security update
Debian DSA Debian DSA DSA-5034-1 thunderbird security update
EUVD EUVD EUVD-2021-24959 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.
Ubuntu USN Ubuntu USN USN-5131-1 Firefox vulnerabilities
Ubuntu USN Ubuntu USN USN-5152-1 Thunderbird vulnerabilities
Ubuntu USN Ubuntu USN USN-5248-1 Thunderbird vulnerabilities
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

No history.

cve-icon MITRE

Status: PUBLISHED

Assigner: mozilla

Published:

Updated: 2024-08-04T01:44:23.527Z

Reserved: 2021-08-10T00:00:00

Link: CVE-2021-38507

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Modified

Published: 2021-12-08T22:15:08.947

Modified: 2024-11-21T06:17:16.447

Link: CVE-2021-38507

cve-icon Redhat

Severity : Important

Publid Date: 2021-11-02T00:00:00Z

Links: CVE-2021-38507 - Bugzilla

cve-icon OpenCVE Enrichment

No data.