CVE-2026-4720

Name: CVE-2026-4720
Creator: NVD / NIST
Published: 2026-03-24T13:16:07.893+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 0.42%

Last modified Jun 17, 2026

CVE-2026-4720 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. Memory safety bugs present in Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. EPSS estimates a 0.42% chance of exploitation in the next 30 days.

Description

Memory safety bugs present in Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Metrics

CVSS 3.1

9.8/10

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

EPSS Probability

0.42%

33.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-120

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 140.9.0
Mozilla	Firefox	< 149.0
Mozilla	Thunderbird	< 140.9.0
Mozilla	Thunderbird	< 149.0

References

https://bugzilla.mozilla.org/buglist.cgi?bug_id=2004652%2C2019372%2C2021922%2C2022567%2C2022733Broken Link
https://www.mozilla.org/security/advisories/mfsa2026-20/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-22/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-23/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-24/Vendor Advisory

Timeline

Published: Mar 24, 2026
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2026-4720?

How severe is CVE-2026-4720?

CVE-2026-4720 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 0.42% probability of exploitation in the next 30 days.

How do I fix CVE-2026-4720?

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-2026-4720?

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

Scan your code now

Source: NVD / NIST