CVE-2021-38507
First published: Tue Nov 02 2021(Updated: )
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.
Credit: security@mozilla.org
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Mozilla Firefox ESR | <91.3 | 91.3 |
| <94 | 94 | |
| <91.3 | 91.3 | |
| <91.3 | 91.3 | |
| Mozilla Firefox | <94.0 | |
| Mozilla Firefox ESR | <91.3.0 | |
| Mozilla Thunderbird | <91.3.0 | |
| Debian Debian Linux | =9.0 | |
| Debian Debian Linux | =10.0 | |
| Debian Debian Linux | =11.0 | |
| debian/firefox | 118.0.2-1 | |
| debian/firefox-esr | 91.12.0esr-1~deb10u1 115.3.1esr-1~deb10u1 102.15.0esr-1~deb11u1 115.3.1esr-1~deb11u1 102.15.1esr-1~deb12u1 115.3.0esr-1~deb12u1 115.3.0esr-1 115.4.0esr-1 | |
| debian/thunderbird | 1:91.12.0-1~deb10u1 1:115.3.1-1~deb10u1 1:102.13.1-1~deb11u1 1:115.3.1-1~deb11u1 1:102.15.1-1~deb12u1 1:115.3.1-1~deb12u1 1:115.3.1-1 |
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Reference Links
- https://bugzilla.mozilla.org/show_bug.cgi?id=1730935
- https://www.mozilla.org/en-US/security/advisories/mfsa2021-49/
- https://www.mozilla.org/en-US/security/advisories/mfsa2021-48/
- https://www.mozilla.org/en-US/security/advisories/mfsa2021-50/
- https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
- https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
- https://security.gentoo.org/glsa/202202-03
- https://security.gentoo.org/glsa/202208-14
- https://www.debian.org/security/2021/dsa-5026
- https://www.debian.org/security/2022/dsa-5034
- https://www.mozilla.org/security/advisories/mfsa2021-48/
- https://www.mozilla.org/security/advisories/mfsa2021-49/
- https://www.mozilla.org/security/advisories/mfsa2021-50/
- https://www.mozilla.org/en-US/security/advisories/mfsa2021-48/#CVE-2021-38507
- https://www.mozilla.org/en-US/security/advisories/mfsa2021-49/#CVE-2021-38507
- https://www.mozilla.org/en-US/security/advisories/mfsa2021-50/#CVE-2021-38507
- https://security-tracker.debian.org/tracker/CVE-2021-38507
Peer vulnerabilities
(Found alongside the following vulnerabilities)
Frequently Asked Questions
What is CVE-2021-38507?
CVE-2021-38507 is a vulnerability in the Opportunistic Encryption feature of HTTP2 that allows a connection to be upgraded to TLS while retaining the visual properties of an HTTP connection.
Which software is affected by CVE-2021-38507?
CVE-2021-38507 affects Mozilla Firefox, Mozilla Firefox ESR, Mozilla Thunderbird, and Debian Linux.
What is the severity of CVE-2021-38507?
CVE-2021-38507 has a severity rating of 6.5 (high).
How can I fix CVE-2021-38507?
To fix CVE-2021-38507, it is recommended to update to the latest version of the affected software.
Where can I find more information about CVE-2021-38507?
You can find more information about CVE-2021-38507 in the references provided: Bugzilla, Mozilla Security Advisories, and Debian LTS Announce.
- collector/mozilla-advisory
- collector/security-tracker-debian
- agent/type
- agent/last-modified-date
- agent/first-publish-date
- agent/softwarecombine
- source/Mozilla
- agent/software-canonical-lookup
- agent/weakness
- agent/author
- agent/severity
- agent/references
- agent/event
- agent/description
- agent/software-canonical-lookup-request
- agent/tags
- collector/nvd-index
- collector/mitre-cve
- source/MITRE
- vendor/mozilla
- canonical/mozilla firefox esr
- package-manager/debian
- canonical/mozilla thunderbird
- canonical/mozilla firefox
- vendor/debian
- canonical/debian debian linux
- version/debian debian linux/9.0
- version/debian debian linux/10.0
- version/debian debian linux/11.0