CVE-2020-26950

Name: CVE-2020-26950
Creator: NVD / NIST
Published: 2020-12-09T01:15:12.503+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.8/10EPSS 42.60%

Last modified Jun 17, 2026

CVE-2020-26950 is a high-severity vulnerability rated 8.8/10 on the CVSS scale. In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting in an exploitable use-after-free condition. This vulnerability affects Firefox < 82.0.3, Firefox ESR < 78.4.1, and Thunderbird < 78.4.2.. EPSS estimates a 42.60% chance of exploitation in the next 30 days.

Description

In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting in an exploitable use-after-free condition. This vulnerability affects Firefox < 82.0.3, Firefox ESR < 78.4.1, and Thunderbird < 78.4.2.

Metrics

CVSS 3.1

8.8/10

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

EPSS Probability

42.60%

98.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-416

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 82.0.3
Mozilla	Firefox Esr	< 78.4.1
Mozilla	Thunderbird	< 78.4.2

References

http://packetstormsecurity.com/files/166175/Firefox-MCallGetProperty-Write-Side-Effects-Use-After-Free.htmlExploit, Third Party Advisory, VDB Entry
https://bugzilla.mozilla.org/show_bug.cgi?id=1675905Exploit, Issue Tracking, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-49/Vendor Advisory
http://packetstormsecurity.com/files/166175/Firefox-MCallGetProperty-Write-Side-Effects-Use-After-Free.htmlExploit, Third Party Advisory, VDB Entry
https://bugzilla.mozilla.org/show_bug.cgi?id=1675905Exploit, Issue Tracking, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-49/Vendor Advisory

Timeline

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

Frequently Asked Questions

What is CVE-2020-26950?

How severe is CVE-2020-26950?

CVE-2020-26950 has a CVSS score of 8.8/10 (HIGH severity). The EPSS model estimates a 42.60% probability of exploitation in the next 30 days.

How do I fix CVE-2020-26950?

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-2020-26950?

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

Scan your code now

Source: NVD / NIST