# CVE-2020-35112: Firefox ESR and 2 others: If a user downloaded a file lacking an extension on Windows, and then "Open"-ed it from the downloads…

CVE-2020-35112 is fixed in 2 products on 1 platform, first by Mozilla Thunderbird (en-US) 78.10.0, released April 15, 2021. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2020-35112
- Priority: High
- CVSS: 8.8
- EPSS: 0.0127
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jan 7, 2021
- Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2020-35112

## Description

If a user downloaded a file lacking an extension on Windows, and then "Open"-ed it from the downloads panel, if there was an executable file in the downloads directory with the same name but with an executable extension (such as .bat or .exe) that executable would have been launched instead. *Note: This issue only affected Windows operating systems. Other operating systems are unaffected.*. This vulnerability affects Firefox < 84, Thunderbird < 78.6, and Firefox ESR < 78.6.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Windows apps | Mozilla Firefox ESR (en-US) | 91.0 | [Mozilla Firefox ESR (en-US) 91.0](https://patchblox.com/security/data/fix/windows-app/mozilla.firefox.esr-91.0.md) | Aug 4, 2021 |
| Windows apps | Mozilla Thunderbird (en-US) | 78.10.0 | [Mozilla Thunderbird (en-US) 78.10.0](https://patchblox.com/security/data/fix/windows-app/mozilla.thunderbird-78.10.0.md) | Apr 15, 2021 |

---

Data as of 2026-11-08T00:53:09Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.