CVE-2025-6435 — Unrestricted File Upload in Mozilla Firefox

CWE-434 — Unrestricted File Upload9 documents8 sources
Severity
8.1HIGHNVD
EPSS
0.1%
top 65.92%
CISA KEV
Not in KEV
Exploit
No known exploits
Affected products
2
Mozilla FirefoxMozilla Thunderbird
Timeline
PublishedJun 24
Latest updateFeb 2

Description

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.

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:HExploitability: 2.2 | Impact: 5.9

Affected Packages3 packages

▶NVDmozilla/firefox< 140.0
▶NVDmozilla/thunderbird< 140.0
▶Ubuntumozilla/thunderbird< 1:140.7.1+build1-0ubuntu0.22.04.1

🔴Vulnerability Details

3
GHSA
GHSA-frfp-c23m-c888: 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 `↗2025-06-26
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OSV
CVE-2025-6435: 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 `↗2025-06-24
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CVEList
Save as in Devtools could download files without sanitizing the extension↗2025-06-24
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📋Vendor Advisories

5
Ubuntu
Thunderbird vulnerabilities↗2026-02-02
▶
Red Hat
firefox: Save as in Devtools could download files without sanitizing the extension↗2025-06-24
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Debian
CVE-2025-6435: firefox - If a user saved a response from the Network tab in Devtools using the Save As co...↗2025
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Mozilla
Mozilla Foundation Security Advisory 2025-54: CVE-2025-6435↗
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Mozilla
Mozilla Foundation Security Advisory 2025-51: CVE-2025-6435↗
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CVE-2025-6435 — Unrestricted File Upload in Mozilla | cvebase