CVE-2021-38507
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.
How to fix
- mozilla firefox94.0 or later
- mozilla firefox_esr91.3.0 or later
- mozilla thunderbird91.3.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mozilla firefox | v < 94.0 | 94.0 |
| mozilla firefox_esr | v < 91.3.0 | 91.3.0 |
| mozilla thunderbird | v < 91.3.0 | 91.3.0 |
| debian debian_linux | 9.0, 10.0, 11.0 | — |
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