CVE-2021-38507
6.5 · MEDIUMOverview
CVE-2021-38507 is a medium-severity vulnerability affecting mozilla firefox. 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 and patches from mozilla. Update firefox to the latest patched version. 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.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| mozilla | firefox | >= 0, < 94.0 | Affected |
| mozilla | firefox_esr | >= 0, < 91.3.0 | Affected |
| mozilla | thunderbird | >= 0, < 91.3.0 | Affected |
References
Frequently Asked Questions
What is CVE-2021-38507?
CVE-2021-38507 is a medium-severity vulnerability affecting mozilla firefox. 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 and patches from mozilla. Update firefox to the latest patched version. 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's AI-powered security agents can automatically detect CVE-2021-38507 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
Automated penetration testing that runs continuously, not just quarterly.
AI-driven PR review catches vulnerable dependencies before they ship.
Browser-based exploitation validates findings with real proof-of-concept.
Related MEDIUM CVEs from 2021
View all →Improper Neutralization of Special Elements used in a Command ('Command Injection') vulnerability in
Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is
Integer Overflow in memory allocating functions. Zephyr versions >= 1.14.2, >= 2.4.0 contain Integer
Magento versions 2.4.2 (and earlier), 2.4.1-p1 (and earlier) and 2.3.6-p1 (and earlier) are affected
Certain NETGEAR devices are affected by out-of-bounds reads and writes. This affects R6400 before 1.
NETGEAR R6400 devices before 1.0.1.70 are affected by a stack-based buffer overflow by an authentica
Next.js is an open source website development framework to be used with the React library. In affect
Authenticated Stored Cross-Site Scripting (XSS) vulnerability in YITH Maintenance Mode (WordPress pl
Multiple Authenticated Stored Cross-Site Scripting (XSS) vulnerabilities in YITH Maintenance Mode (W
An attacker with physical access to Boston Scientific Zoom Latitude Model 3120 can remove the hard d
Grafana is an open-source platform for monitoring and observability. In affected versions if an atta
A cross-site scripting (XSS) vulnerability has been reported to affect QNAP device running QmailAgen