Cyber Posture

CVE-2026-2778

Critical

Published: 24 February 2026

Published
24 February 2026
Modified
13 April 2026
KEV Added
—
Patch
—
CVSS Score 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
EPSS Score 0.0003 8.2th percentile
Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

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.

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match
prevent

Directly mandates identification, reporting, and correction of the sandbox escape flaw through patching to the fixed Firefox 148, ESR 115.33/140.8, and Thunderbird versions.

RA-5 Vulnerability Monitoring and Scanning partial match
prevent

Vulnerability scanning detects systems running vulnerable Firefox and Thunderbird versions affected by the DOM boundary condition flaw.

SI-5 Security Alerts, Advisories, and Directives partial match
prevent

Requires receiving and acting on security advisories like Mozilla MFSA 2026-13 to enable timely patching of CVE-2026-2778.

Security SummaryAI

CVE-2026-2778 is a sandbox escape vulnerability stemming from incorrect boundary conditions in the DOM: Core & HTML component of Mozilla Firefox and Thunderbird. It affects versions of Firefox prior to 148, Firefox ESR prior to 115.33 and 140.8, and Thunderbird prior to 148 and 140.8. The issue is classified under CWE-119 (improper restriction of operations within the bounds of a memory buffer) with a supporting NVD-CWE-noinfo mapping, and it carries a maximum CVSS v3.1 base score of 10.0.

Remote attackers can exploit this vulnerability over the network with low complexity, requiring no privileges, authentication, or user interaction. The attack vector leverages a changed scope (S:C), enabling high-impact consequences across confidentiality, integrity, and availability (C:H/I:H/A:H). Successful exploitation allows attackers to escape the browser sandbox, potentially granting arbitrary code execution on the host system.

Mozilla's security advisories (MFSA 2026-13 through 2026-16) and the associated Bugzilla entry (bug 2016358) detail the patch deployment in the specified fixed releases. Security practitioners should prioritize updating affected Firefox and Thunderbird installations to mitigate this critical issue, as no workarounds are mentioned in the provided references.

Details

CWE(s)
NVD-CWE-noinfoCWE-119

Affected Products

mozilla
firefox
≤ 115.33.0 · ≤ 148.0 · 128.0 — 140.8.0
mozilla
thunderbird
≤ 140.8.0 · ≤ 148.0

MITRE ATT&CK Enterprise TechniquesAI

T1189 Drive-by Compromise Initial Access
Adversaries may gain access to a system through a user visiting a website over the normal course of browsing.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
Why these techniques?

Sandbox escape via memory corruption (CWE-119) in browser DOM enables remote no-interaction client RCE, directly mapping to drive-by compromise (T1189), exploitation for client execution (T1203), and privilege escalation out of the restricted sandbox (T1068).

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

References