CVE-2021-38506 Security feature bypass in Firefox

What is CVE-2021-38506?

CVE-2021-38506 is a medium-severity vulnerability in Debian Debian Linux, published on 8 Dec 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

Through a series of navigations, Firefox could have entered fullscreen mode without notification or warning to the user. This could lead to spoofing attacks on the browser UI including phishing. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.

Weakness: CWE-1021

Which versions are affected by CVE-2021-38506?

It affects 4 products.

Products include Debian Debian Linux, Mozilla Firefox, Mozilla Firefox Esr, Mozilla Thunderbird.

How do I fix CVE-2021-38506?

Upgrade to a fixed version.

Is CVE-2021-38506 being exploited?

There is no known exploitation of CVE-2021-38506 in the wild and no public exploit code.

Other vulnerabilities in Debian Debian Linux

• CVE-2015-3306 ProFTPD Improper Access Control Exploited Critical 10.0
• CVE-2025-49113 RoundCube Webmail Deserialization of Untrusted Data Exploited Critical 9.9
• CVE-2026-24061 GNU InetUtils Argument Injection Exploited Critical 9.8
• CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Exploited Critical 9.8
• CVE-2024-9680 Mozilla Firefox Use-After-Free Exploited Critical 9.8

All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2021-38506, GHSA-9wxw-f5fm-cf3j, UBUNTU-CVE-2021-38506.