CVE-2026-0879
Published: 13 January 2026
Summary
CVE-2026-0879 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 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 41.8th 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-2026-0879 is a sandbox escape vulnerability stemming from incorrect boundary conditions (CWE-119) in the Graphics component of Mozilla products. It affects Firefox versions prior to 147, Firefox ESR prior to 115.32 and 140.7, Thunderbird prior to 147, and Thunderbird prior to 140.7. The issue was publicly disclosed on January 13, 2026, and carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), indicating critical severity due to its potential for high-impact exploitation.
Remote attackers can exploit this vulnerability over the network with low complexity, requiring no privileges, no user interaction, and no change in scope. Successful exploitation enables high confidentiality, integrity, and availability impacts, allowing attackers to escape the browser sandbox and potentially execute arbitrary code on the victim's system, such as through malicious web content or graphics files processed by the affected component.
Mozilla's security advisories (MFSA 2026-01 through 2026-04) and the associated Bugzilla entry (bug 2004602) detail the fix applied in the listed versions. Security practitioners should prioritize updating affected Firefox and Thunderbird installations to mitigate the risk, as no workarounds are specified in the provided references.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2085
Vulnerability details
Sandbox escape due to incorrect boundary conditions in the Graphics component. This vulnerability was fixed in Firefox 147, Firefox ESR 115.32, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Sandbox escape in browser graphics component directly enables drive-by compromise via malicious web content and exploitation for client-side arbitrary code execution.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
SI-2 mandates timely identification, reporting, and correction of critical flaws like this graphics component sandbox escape via patching to fixed Firefox and Thunderbird versions.
SI-5 requires receiving and acting on vendor security advisories such as Mozilla's MFSA 2026-01 through 2026-04 detailing this CVE and its patches.
RA-5 supports vulnerability scanning to identify systems with vulnerable pre-147 Firefox or pre-140.7 ESR versions affected by this boundary condition error.