#VU57881 Security features bypass in Mozilla Firefox and Firefox ESR - CVE-2021-38507

Description

The vulnerability allows a remote attacker to bypass implemented security restrictions.

The vulnerability exists in the Opportunistic Encryption feature of HTTP2, which 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 from port 443 to port 8443, causing the browser to treat the content of port 8443 as same-origin with HTTP. As a result, a remote attacker can bypass Same-Origin-Policy on services hosted on other ports.

Remediation

External links

• https://www.mozilla.org/en-US/security/advisories/mfsa2021-48/
• https://www.mozilla.org/en-US/security/advisories/mfsa2021-49/