# Mozilla Firefox (en-US) 121.0

Mozilla Firefox (en-US) 121.0, released December 20, 2023, fixes 15 CVEs in Mozilla Firefox (en-US). None of them is reported as exploited. Patch Radar priority: High. The latest Mozilla Firefox (en-US) is 159.0, which also fixes every one of these CVEs.

- Web page: https://patchblox.com/security/fix/windows-app/mozilla.firefox-121.0
- Platform: Windows apps
- Released: Dec 20, 2023
- Priority: High (Closes CVE-2023-6856, high severity)
- CVEs: 15, exploited: 0, on CISA KEV: 0
- Superseded by: [Mozilla Firefox (en-US) 159.0](https://patchblox.com/security/data/product/windows-app/mozilla-firefox-en-us.md), the latest version, which also fixes every CVE listed here

## Applies to

| Product | Release | Fixed in |
|---|---|---|
| [Mozilla Firefox (en-US)](https://patchblox.com/security/data/product/windows-app/mozilla-firefox-en-us.md) |  | 121.0 |

## CVEs this fix closes

| CVE | Priority | Title | CVSS | EPSS | Exploitation |
|---|---|---|---:|---:|---|
| [CVE-2023-6856](https://patchblox.com/security/data/cve/CVE-2023-6856.md) | High | Mozilla Firefox ESR and 5 others: The WebGL `DrawElementsInstanced` method was susceptible to a heap buffer overflow when used on systems… | 8.8 | 0.2063 |  |
| [CVE-2023-6858](https://patchblox.com/security/data/cve/CVE-2023-6858.md) | High | Mozilla Firefox ESR and 5 others: Out-of-bounds Write | 8.8 | 0.0154 |  |
| [CVE-2023-6861](https://patchblox.com/security/data/cve/CVE-2023-6861.md) | High | Mozilla Firefox ESR and 5 others: The `nsWindow::PickerOpen(void)` method was susceptible to a heap buffer overflow when running in headless… | 8.8 | 0.0141 |  |
| [CVE-2023-6864](https://patchblox.com/security/data/cve/CVE-2023-6864.md) | High | Mozilla Firefox ESR and 5 others: Memory safety bugs present in Firefox 120, Firefox ESR 115.5, and Thunderbird 115.5. | 8.8 | 0.0119 |  |
| [CVE-2023-6859](https://patchblox.com/security/data/cve/CVE-2023-6859.md) | High | Mozilla Firefox ESR and 5 others: A use-after-free condition affected TLS socket creation when under memory pressure. | 8.8 | 0.0109 |  |
| [CVE-2023-6863](https://patchblox.com/security/data/cve/CVE-2023-6863.md) | High | Mozilla Firefox ESR and 5 others: The `ShutdownObserver()` was susceptible to potentially undefined behavior due to its reliance on a dynamic… | 8.8 | 0.0104 |  |
| [CVE-2023-6865](https://patchblox.com/security/data/cve/CVE-2023-6865.md) | High | Mozilla Firefox ESR and 3 others: `EncryptingOutputStream` was susceptible to exposing uninitialized data. | 7.5 | 0.0089 |  |
| [CVE-2023-6873](https://patchblox.com/security/data/cve/CVE-2023-6873.md) | High | Mozilla Firefox ESR and 3 others: Memory safety bugs present in Firefox 120. | 8.8 | 0.0085 |  |
| [CVE-2023-6866](https://patchblox.com/security/data/cve/CVE-2023-6866.md) | High | Mozilla Firefox ESR and 3 others: TypedArrays can be fallible and lacked proper exception handling. | 8.8 | 0.0068 |  |
| [CVE-2023-6860](https://patchblox.com/security/data/cve/CVE-2023-6860.md) | Routine | Mozilla Firefox ESR and 5 others: The `VideoBridge` allowed any content process to use textures produced by remote decoders. | 6.5 | 0.0096 |  |
| [CVE-2023-6135](https://patchblox.com/security/data/cve/CVE-2023-6135.md) | Routine | Mozilla Firefox ESR and 3 others: Multiple NSS NIST curves were susceptible to a side-channel attack known as "Minerva". | 4.3 | 0.0071 |  |
| [CVE-2023-6867](https://patchblox.com/security/data/cve/CVE-2023-6867.md) | Routine | Mozilla Firefox ESR and 3 others: The timing of a button click causing a popup to disappear was approximately the same length as the anti-clickjacking… | 6.1 | 0.0068 |  |
| [CVE-2023-6872](https://patchblox.com/security/data/cve/CVE-2023-6872.md) | Routine | Mozilla Firefox ESR and 3 others: Browser tab titles were being leaked by GNOME to system logs. | 6.5 | 0.0065 |  |
| [CVE-2023-6869](https://patchblox.com/security/data/cve/CVE-2023-6869.md) | Routine | Mozilla Firefox ESR and 3 others: A `<dialog>` element could have been manipulated to paint content outside of a sandboxed iframe. | 6.5 | 0.0056 |  |
| [CVE-2023-6871](https://patchblox.com/security/data/cve/CVE-2023-6871.md) | Routine | Mozilla Firefox ESR and 3 others: Under certain conditions, Firefox did not display a warning when a user attempted to navigate to a new… | 4.3 | 0.0049 |  |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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