CVE-2026-2778
Published: 24 February 2026
Summary
CVE-2026-2778 is a critical-severity Improper Restriction of Operations within the Bounds of a Memory Buffer (CWE-119) vulnerability in Mozilla Firefox. Its CVSS base score is 10.0 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 38.1th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and RA-5 (Vulnerability Monitoring and Scanning).
Deeper analysis
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.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8500
Vulnerability details
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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
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).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
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.
Vulnerability scanning detects systems running vulnerable Firefox and Thunderbird versions affected by the DOM boundary condition flaw.
Requires receiving and acting on security advisories like Mozilla MFSA 2026-13 to enable timely patching of CVE-2026-2778.