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CVE-2021-38507
Date: December 8, 2021
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.
Severity Score
Related Resources (16)
Severity Score
Weakness Type (CWE)
Origin Validation Error
CWE-346CVSS v3.1
Base Score: |
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Attack Vector (AV): | NETWORK |
Attack Complexity (AC): | LOW |
Privileges Required (PR): | NONE |
User Interaction (UI): | REQUIRED |
Scope (S): | UNCHANGED |
Confidentiality (C): | NONE |
Integrity (I): | HIGH |
Availability (A): | NONE |
CVSS v2
Base Score: |
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Access Vector (AV): | NETWORK |
Access Complexity (AC): | MEDIUM |
Authentication (AU): | NONE |
Confidentiality (C): | NONE |
Integrity (I): | PARTIAL |
Availability (A): | NONE |
Additional information: |