How severe is CVE-2021-38507?

This vulnerability has a severity rating of MEDIUM with a CVSS score of 6.5 out of 10.

What type of vulnerability is CVE-2021-38507?

This is classified as CWE-346, which is a common weakness in software security.

CVE-2021-38507 - MEDIUM Severity | CVSS 6.5

Vulnerability 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.

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