Mozilla Firefox (en-US) 155.0
Mozilla Firefox (en-US) 155.0, released September 1, 2026, fixes 26 CVEs in Mozilla Firefox (en-US). None of them is reported as exploited. Patch Radar priority: Urgent. The latest Mozilla Firefox (en-US) is 159.0, which also fixes every one of these CVEs.
Superseded. The latest Mozilla Firefox (en-US) is 159.0, which also fixes every CVE on this page. Install that instead.
Priority of the 26 CVEs
Applies to
| Product | Version |
|---|---|
| Mozilla Firefox (en-US) | 155.0 |
CVEs this fix closes
| Priority | CVE | Title | CVSS | EPSS | Exploitation |
|---|---|---|---|---|---|
| Urgent | CVE-2026-84134 | Other issue in the Profile Backup component | 9.8 | 0.0057 | None reported |
| Urgent | CVE-2026-84142 | Internally found bugs fixed in Thunderbird 155 | 9.8 | 0.0056 | None reported |
| Urgent | CVE-2026-84143 | Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15 | 9.8 | 0.0038 | None reported |
| Urgent | CVE-2026-84119 | Sandbox escape due to use-after-free in the DOM: Navigation component | 9.6 | 0.0032 | None reported |
| Urgent | CVE-2026-84121 | Sandbox escape due to use-after-free in the DOM: Security component | 9.6 | 0.0032 | None reported |
| High | CVE-2026-84130 | Information disclosure in the Graphics: WebGPU component | 7.5 | 0.0044 | None reported |
| High | CVE-2026-84128 | Privilege escalation in the WebDriver BiDi component | 8.8 | 0.0044 | None reported |
| High | CVE-2026-84123 | Privilege escalation due to use-after-free in the Graphics: WebGPU component | 8.8 | 0.0044 | None reported |
| High | CVE-2026-84144 | Internally found bugs fixed in Thunderbird 155 and Thunderbird ESR 153.2 | 7.5 | 0.0043 | None reported |
| High | CVE-2026-84145 | Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15 | 7.5 | 0.0037 | None reported |
| High | CVE-2026-84141 | Integer overflow in the Graphics: ImageLib component | 9.8 | 0.0034 | None reported |
| High | CVE-2026-84131 | Privilege escalation due to invalid pointer in the Graphics component | 8.8 | 0.0033 | None reported |
| High | CVE-2026-84132 | Information disclosure in the Networking: HTTP component | 7.5 | 0.0026 | None reported |
| High | CVE-2026-84120 | Use-after-free in the Audio/Video component | 7.5 | 0.0022 | None reported |
| High | CVE-2026-84122 | Use-after-free in the Audio/Video component | 7.5 | 0.0021 | None reported |
| High | CVE-2026-84129 | Site isolation issue in the DOM: Navigation component | 9.8 | 0.0019 | None reported |
| High | CVE-2026-84133 | Site isolation issue in the DOM: Push Subscriptions component | 9.8 | 0.0019 | None reported |
| High | CVE-2026-84140 | Site isolation issue in the DOM: Navigation component | 9.8 | 0.0018 | None reported |
| High | CVE-2026-84124 | Use-after-free in the DOM: Core & HTML component | 8.8 | 0.0017 | None reported |
| Routine | CVE-2026-84138 | Denial-of-service in the PDF Viewer component | 6.5 | 0.0037 | None reported |
| Routine | CVE-2026-84139 | Clickjacking issue in the DOM: Events component | 6.1 | 0.0034 | None reported |
| Routine | CVE-2026-84126 | Incorrect boundary conditions in the Layout: Grid component | 4.3 | 0.0031 | None reported |
| Routine | CVE-2026-84118 | Use-after-free in the JavaScript: GC component | 5.4 | 0.0029 | None reported |
| Routine | CVE-2026-84125 | Use-after-free in the DOM: Core & HTML component | 5.4 | 0.0029 | None reported |
| Routine | CVE-2026-84136 | Other issue in the DOM: Navigation component | 6.1 | 0.0020 | None reported |
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