CVE-2021-38492

Name: CVE-2021-38492
Creator: NVD / NIST
Published: 2021-11-03T01:15:07.2+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 1.12%

Last modified Jun 17, 2026

CVE-2021-38492 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. 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. EPSS estimates a 1.12% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

6.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

EPSS Probability

1.12%

62.0th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 92.0
Mozilla	Firefox	>= 91.0, < 91.1
Mozilla	Firefox Esr	< 78.14
Mozilla	Thunderbird	< 78.14
Mozilla	Thunderbird	>= 91.0, < 91.1

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1721107Exploit, Issue Tracking, Vendor Advisory
https://security.gentoo.org/glsa/202208-14Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-38/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-39/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-40/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-41/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-42/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1721107Exploit, Issue Tracking, Vendor Advisory
https://security.gentoo.org/glsa/202208-14Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-38/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-39/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-40/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-41/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-42/Vendor Advisory

Timeline

Published: Nov 3, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-38492?

How severe is CVE-2021-38492?

CVE-2021-38492 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 1.12% probability of exploitation in the next 30 days.

How do I fix CVE-2021-38492?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-38492?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST