CVE-2026-2778

Name: CVE-2026-2778
Creator: NVD / NIST
Published: 2026-02-24T14:16:26.23+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 10/10EPSS 0.49%

Last modified Jun 17, 2026

CVE-2026-2778 is a critical-severity vulnerability rated 10/10 on the CVSS scale. Sandbox escape due to incorrect boundary conditions in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.. EPSS estimates a 0.49% chance of exploitation in the next 30 days.

Description

Sandbox escape due to incorrect boundary conditions in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Metrics

CVSS 3.1

10/10

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

EPSS Probability

0.49%

38.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-119

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 115.33.0
Mozilla	Firefox	< 148.0
Mozilla	Firefox	>= 128.0, < 140.8.0
Mozilla	Thunderbird	< 140.8.0
Mozilla	Thunderbird	< 148.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2016358Issue Tracking, Permissions Required
https://www.mozilla.org/security/advisories/mfsa2026-13/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-14/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-15/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-16/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-17/Vendor Advisory

Timeline

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

Frequently Asked Questions

What is CVE-2026-2778?

How severe is CVE-2026-2778?

CVE-2026-2778 has a CVSS score of 10/10 (CRITICAL severity). The EPSS model estimates a 0.49% probability of exploitation in the next 30 days.

How do I fix CVE-2026-2778?

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-2026-2778?

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

Scan your code now

Source: NVD / NIST