CVE-2020-26951

Name: CVE-2020-26951
Creator: NVD / NIST
Published: 2020-12-09T01:15:12.643+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.1/10EPSS 1.04%

Last modified Jun 17, 2026

CVE-2020-26951 is a medium-severity vulnerability rated 6.1/10 on the CVSS scale. A parsing and event loading mismatch in Firefox's SVG code could have allowed load events to fire, even after sanitization. An attacker already capable of exploiting an XSS vulnerability in privileged internal pages could have used this attack to bypass our built-in sanitizer. EPSS estimates a 1.04% chance of exploitation in the next 30 days.

Description

A parsing and event loading mismatch in Firefox's SVG code could have allowed load events to fire, even after sanitization. An attacker already capable of exploiting an XSS vulnerability in privileged internal pages could have used this attack to bypass our built-in sanitizer. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

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

1.04%

59.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-79

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 83.0
Mozilla	Firefox Esr	< 78.5
Mozilla	Thunderbird	< 78.5

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1667113Issue Tracking, Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-50/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-51/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-52/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1667113Issue Tracking, Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-50/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-51/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-52/Vendor Advisory

Timeline

Published: Dec 9, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2020-26951?

How severe is CVE-2020-26951?

CVE-2020-26951 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 1.04% probability of exploitation in the next 30 days.

How do I fix CVE-2020-26951?

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-2020-26951?

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

Scan your code now

Source: NVD / NIST