Mozilla Firefox ESR Security Advisory: Multiple High-Severity Vulnerabilities (Sandbox Escape/UAF)

Advisory ID: Mozilla Foundation Security Advisory 2026-03 Release Date: January 13, 2026 Severity: High Affected Products: Firefox ESR, Firefox ESR 140.7 Vulnerability List 1. CVE-2026-0877 - Description: Mitigation bypass in the DOM: Security component - Reporter: mingjung - Severity: High - Reference: Bug 1999257 2. CVE-2026-0878 - Description: Sandbox escape due to incorrect boundary conditions in the Graphics: CanvasWebGL component - Reporter: Oskar L - Severity: High - Reference: Bug 2003989 3. CVE-2026-0879 - Description: Sandbox escape due to incorrect boundary conditions in the Graphics component - Reporter: Oskar L - Severity: High - Reference: Bug 2004602 4. CVE-2026-0880 - Description: Sandbox escape due to integer overflow in the Graphics component - Reporter: Oskar L - Severity: High - Reference: Bug 2005014 5. CVE-2026-0882 - Description: Use-after-free in the IPC component - Reporter: Randell Jesup - Severity: High - Reference: Bug 1924125 6. CVE-2025-14327 - Description: Spoofing issue in the Downloads Panel component - Reporter: Caro Kann - Severity: Moderate - Reference: Bug 1970743 7. CVE-2026-0883 - Description: Information disclosure in the Networking component - Reporter: Vladislav Plyatsok - Severity: Moderate - Reference: Bug 1989340 8. CVE-2026-0884 - Description: Use-after-free in the JavaScript Engine component - Reporter: Gary Kwong and Nan Wang - Severity: Moderate - Reference: Bug 2003588 9. CVE-2026-0885 - Description: Use-after-free in the JavaScript: GC component - Reporter: Irvan Kurniawan - Severity: Moderate - Reference: Bug 2003607 10. CVE-2026-0886 - Description: Incorrect boundary conditions in the Graphics component - Reporter: Oskar L - Severity: Moderate - Reference: Bug 2005658 11. CVE-2026-0887 - Description: Clickjacking issue, information disclosure in the PDF Viewer component - Reporter: Lyra Rebane - Severity: Moderate - Reference: Bug 2006500 12. CVE-2026-0890 - Description: Spoofing issue in the DOM: Copy & Paste and Drag & Drop component - Reporter: Edgar Chen - Severity: Low - Reference: Bug 2005081 13. CVE-2026-0891 - Description: Memory safety bugs fixed in Firefox ESR 140.7, Thunderbird ESR 140.7, Firefox 147 and Thunderbird 147 - Reporter: Andrew McCreight, Dennis Jackson and the Mozilla Fuzzing Team - Severity: High - Additional Description: Memory safety bugs present in Firefox ESR 140.6, Thunderbird ESR 140.6, Firefox 146 and Thunderbird 146. 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. - Reference: Memory safety bugs fixed in Firefox ESR 140.7, Thunderbird ESR 140.7, Firefox 147 and Thunderbird 147

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Mozilla Firefox ESR Security Advisory: Multiple High-Severity Vulnerabilities (Sandbox Escape/UAF)