---
id: CVE-2025-6435
title: >-
  If a user saved a response from the Network tab in Devtools using the Save As
  context menu option, that file may not have been saved with the `.download`
  file extension
summary: >-
  If a user saved a response from the Network tab in Devtools using the Save As
  context menu option, that file may not have been saved with the `.download`
  file extension. This could have led to the user inadvertently running a
  malicious e…
severity: high
cvss: 8.1
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-434
vendor: mozilla
product: firefox
affected:
  - firefox < 140.0
  - thunderbird < 140.0
patched:
  - firefox 140.0
  - thunderbird 140.0
published: '2025-06-24'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T18:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-6435'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1950056'
    label: security@mozilla.org
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1961777'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-51/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-54/'
    label: security@mozilla.org
tags:
  - nvd
epss: 0.00457
epssPercentile: 0.37292
ingestedAt: '2026-09-30T18:17:24.446Z'
---

## Overview

If a user saved a response from the Network tab in Devtools using the Save As context menu option, that file may not have been saved with the `.download` file extension. This could have led to the user inadvertently running a malicious executable. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

## Affected

- `firefox < 140.0`
- `thunderbird < 140.0`

## Remediation

Upgrade past the affected range:

- `firefox 140.0`
- `thunderbird 140.0`