What’s Vulnerable › Vulnerabilities

CVE-2021-38492

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.2% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-11-03 · updated 2026-06-17

Description

When delegating navigations to the operating system, Firefox would accept the `mk` scheme which might allow attackers to launch pages and execute scripts in Internet Explorer in unprivileged mode. *This bug only affects Firefox for Windows. Other operating systems are unaffected.*. This vulnerability affects Firefox < 92, Thunderbird < 91.1, Thunderbird < 78.14, Firefox ESR < 78.14, and Firefox ESR < 91.1.

Affected products

• Mozilla Firefox: before 92.0; from 91.0 before 91.1 — fixed in 91.1, 92.0
• Mozilla Firefox ESR: before 78.14 — fixed in 78.14
• Mozilla Thunderbird: before 78.14; from 91.0 before 91.1 — fixed in 78.14, 91.1

How to fix

Upgrade to a fixed version: Mozilla Firefox 91.1, 92.0; Mozilla Firefox ESR 78.14; Mozilla Thunderbird 78.14, 91.1. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1721107
• https://security.gentoo.org/glsa/202208-14
• https://www.mozilla.org/security/advisories/mfsa2021-38/
• https://www.mozilla.org/security/advisories/mfsa2021-39/
• https://www.mozilla.org/security/advisories/mfsa2021-40/
• https://www.mozilla.org/security/advisories/mfsa2021-41/
• https://www.mozilla.org/security/advisories/mfsa2021-42/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1721107
• https://security.gentoo.org/glsa/202208-14
• https://www.mozilla.org/security/advisories/mfsa2021-38/
• https://www.mozilla.org/security/advisories/mfsa2021-39/
• https://www.mozilla.org/security/advisories/mfsa2021-40/

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