CVE-2021-23986

Name: CVE-2021-23986
Creator: NVD / NIST
Published: 2021-03-31T14:15:19.343+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 0.44%

Last modified Jun 17, 2026

CVE-2021-23986 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. A malicious extension with the 'search' permission could have installed a new search engine whose favicon referenced a cross-origin URL. The response to this cross-origin request could have been read by the extension, allowing a same-origin policy bypass by the extension, which should not have cross-origin permissions. EPSS estimates a 0.44% chance of exploitation in the next 30 days.

Description

A malicious extension with the 'search' permission could have installed a new search engine whose favicon referenced a cross-origin URL. The response to this cross-origin request could have been read by the extension, allowing a same-origin policy bypass by the extension, which should not have cross-origin permissions. This cross-origin request was made without cookies, so the sensitive information disclosed by the violation was limited to local-network resources or resources that perform IP-based authentication. This vulnerability affects Firefox < 87.

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

0.44%

34.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-346

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 87.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1692623Issue Tracking, Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-10/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1692623Issue Tracking, Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-10/Vendor Advisory

Timeline

Published: Mar 31, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-23986?

How severe is CVE-2021-23986?

CVE-2021-23986 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.44% probability of exploitation in the next 30 days.

How do I fix CVE-2021-23986?

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-2021-23986?

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

Scan your code now

Source: NVD / NIST