CVE-2021-23959

Name: CVE-2021-23959
Creator: NVD / NIST
Published: 2021-02-26T03:15:13.853+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.1/10EPSS 0.57%

Last modified Jun 17, 2026

CVE-2021-23959 is a medium-severity vulnerability rated 6.1/10 on the CVSS scale. An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. EPSS estimates a 0.57% chance of exploitation in the next 30 days.

Description

An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

Metrics

CVSS 3.1

6.1/10

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

EPSS Probability

0.57%

42.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-79

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 85.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1659035Issue Tracking, Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-03/Release Notes, Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1659035Issue Tracking, Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-03/Release Notes, Vendor Advisory

Timeline

Published: Feb 26, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-23959?

How severe is CVE-2021-23959?

CVE-2021-23959 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 0.57% probability of exploitation in the next 30 days.

How do I fix CVE-2021-23959?

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-2021-23959?

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

Scan your code now

Source: NVD / NIST