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CVE-2021-38507

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-or…

Published Dec 8, 2021CWE-346EPSS 0.83%

Overview

CVE-2021-38507 is a medium-severity vulnerability. It was published on December 8, 2021 and has a CVSS 3.1 base score of 6.5 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 6.5, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refbugzilla.mozilla.org/show_bug.cgi?id=1730935Reflists.debian.org/debian-lts-announce/2021/12/msg00030.htmlReflists.debian.org/debian-lts-announce/2022/01/msg00001.htmlRefsecurity.gentoo.org/glsa/202202-03Refsecurity.gentoo.org/glsa/202208-14Refwww.debian.org/security/2021/dsa-5026Refwww.debian.org/security/2022/dsa-5034Refwww.mozilla.org/security/advisories/mfsa2021-48/Refwww.mozilla.org/security/advisories/mfsa2021-49/Refwww.mozilla.org/security/advisories/mfsa2021-50/

How CyberStrike helps

Frequently asked questions

What is CVE-2021-38507?

CVE-2021-38507 is a medium-severity vulnerability. It was published on December 8, 2021 and has a CVSS 3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2021-38507?

This vulnerability has a CVSS 3.1 base score of 6.5, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2021-38507?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2021-38507?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-38507 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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