Vulnerability in Mozilla Firefox
CVE-2021-38507
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.
EPSS: 0.008 (51.8th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N.
Affected products
- Mozilla Firefox — versions unspecified
- Mozilla Firefox Esr — versions unspecified
- Mozilla Firefox_esr
- Mozilla Thunderbird — versions unspecified
- Debian Debian_linux — versions 9.0, 10.0, 11.0
Weakness classification (CWE)
References
- security@mozilla.org (x_refsource_MISC, Vendor Advisory)
- security@mozilla.org (x_refsource_MISC, Vendor Advisory)
- security@mozilla.org (x_refsource_MISC, Vendor Advisory)
- security@mozilla.org (Permissions Required, x_refsource_MISC, Issue Tracking, Vendor Advisory)
- security@mozilla.org (vendor-advisory, Third Party Advisory, x_refsource_DEBIAN)
- security@mozilla.org (mailing-list, x_refsource_MLIST, Mailing List, Third Party Advisory)
- security@mozilla.org (vendor-advisory, Third Party Advisory, x_refsource_DEBIAN)
- security@mozilla.org (mailing-list, x_refsource_MLIST, Mailing List, Third Party Advisory)
- security@mozilla.org (vendor-advisory, Third Party Advisory, x_refsource_GENTOO)
- security@mozilla.org (vendor-advisory, Third Party Advisory, x_refsource_GENTOO)
Frequently asked questions
- What is CVE-2021-38507?
- CVE-2021-38507 is a medium-severity vulnerability in Mozilla Firefox, classified under Origin Validation Error. CVSS score: 6.5/10. Published 2021-12-08.
- How severe is CVE-2021-38507?
- Medium severity. CVSS v3 base score is 6.5 out of 10.