CVE-2021-38505

Name: CVE-2021-38505
Creator: NVD / NIST
Published: 2021-12-08T22:15:08.847+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 1.05%

Last modified Jun 17, 2026

CVE-2021-38505 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. Microsoft introduced a new feature in Windows 10 known as Cloud Clipboard which, if enabled, will record data copied to the clipboard to the cloud, and make it available on other computers in certain scenarios. Applications that wish to prevent copied data from being recorded in Cloud History must use specific clipboard formats; and Firefox before versions 94 and ESR 91.3 did not implement them. EPSS estimates a 1.05% chance of exploitation in the next 30 days.

Description

Microsoft introduced a new feature in Windows 10 known as Cloud Clipboard which, if enabled, will record data copied to the clipboard to the cloud, and make it available on other computers in certain scenarios. Applications that wish to prevent copied data from being recorded in Cloud History must use specific clipboard formats; and Firefox before versions 94 and ESR 91.3 did not implement them. This could have caused sensitive data to be recorded to a user's Microsoft account. *This bug only affects Firefox for Windows 10+ with Cloud Clipboard enabled. Other operating systems are unaffected.*. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.

Metrics

CVSS 3.1

6.5/10

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

EPSS Probability

1.05%

59.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-668

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 94.0
Mozilla	Firefox Esr	< 91.3.0
Mozilla	Thunderbird	< 91.3.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1730194Issue Tracking, Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-48/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-49/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-50/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1730194Issue Tracking, Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-48/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-49/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-50/Vendor Advisory

Timeline

Published: Dec 8, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-38505?

How severe is CVE-2021-38505?

CVE-2021-38505 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 1.05% probability of exploitation in the next 30 days.

How do I fix CVE-2021-38505?

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-2021-38505?

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

Scan your code now

Source: NVD / NIST