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.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
OS impact
SUSE Affected 1 release
| Version | Status | Fixed in |
|---|---|---|
| — | Affected | — |
Arch Fixed 1 release
| Version | Status | Fixed in |
|---|---|---|
| — | Fixed | 91.3.0-1 |
Debian Fixed 5 releases
| Version | Status | Fixed in |
|---|---|---|
| trixie | Fixed | 91.3.0esr-1 |
| sid | Fixed | 94.0-1 |
| forky | Fixed | 91.3.0esr-1 |
| bullseye | Fixed | 91.4.1esr-1~deb11u1 |
| bookworm | Fixed | 91.3.0esr-1 |
Red Hat Fixed 1 release
| Version | Status | Fixed in |
|---|---|---|
| 8 | Fixed | — |
Rocky Linux Fixed 1 release
| Version | Status | Fixed in |
|---|---|---|
| 8 | Fixed | — |
References
- https://security.archlinux.org/ASA-202111-3
- https://security.archlinux.org/ASA-202111-2
- https://www.suse.com/security/cve/CVE-2021-38507.html
- https://security-tracker.debian.org/tracker/CVE-2021-38507
- https://errata.rockylinux.org/RLSA-2021:4130
- https://errata.rockylinux.org/RLSA-2021:4123
- https://errata.almalinux.org/8/ALSA-2021-4123.html
- https://errata.almalinux.org/8/ALSA-2021-4130.html
- https://access.redhat.com/errata/RHSA-2021:4123
- https://access.redhat.com/errata/RHSA-2021:4130
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.