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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | < 94.0 |
| Mozilla | Firefox Esr | < 91.3.0 |
| Mozilla | Thunderbird | < 91.3.0 |
| Debian | Debian Linux | 9.0 |
Related Weaknesses (CWE)
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1730935Issue TrackingPermissions RequiredVendor Advisory
- https://lists.debian.org/debian-lts-announce/2021/12/msg00030.htmlMailing ListThird Party Advisory
- https://lists.debian.org/debian-lts-announce/2022/01/msg00001.htmlMailing ListThird Party Advisory
- https://security.gentoo.org/glsa/202202-03Third Party Advisory
- https://security.gentoo.org/glsa/202208-14Third Party Advisory
- https://www.debian.org/security/2021/dsa-5026Third Party Advisory
- https://www.debian.org/security/2022/dsa-5034Third Party Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-48/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-49/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-50/Vendor Advisory
- https://bugzilla.mozilla.org/show_bug.cgi?id=1730935Issue TrackingPermissions RequiredVendor Advisory
- https://lists.debian.org/debian-lts-announce/2021/12/msg00030.htmlMailing ListThird Party Advisory
- https://lists.debian.org/debian-lts-announce/2022/01/msg00001.htmlMailing ListThird Party Advisory
- https://security.gentoo.org/glsa/202202-03Third Party Advisory
- https://security.gentoo.org/glsa/202208-14Third Party Advisory
FAQ
What is CVE-2021-38507?
CVE-2021-38507 is a vulnerability with a CVSS score of 6.5 (MEDIUM). 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-origi...
How severe is CVE-2021-38507?
CVE-2021-38507 has been rated MEDIUM with a CVSS base score of 6.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2021-38507?
Check the references section above for vendor advisories and patch information. Affected products include: Mozilla Firefox, Mozilla Firefox Esr, Mozilla Thunderbird, Debian Debian Linux.