What’s Vulnerable › Vulnerabilities

CVE-2025-6435: Save as in Devtools could download files without sanitizing the extension

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-06-24 · updated 2026-09-30
• Weakness: CWE-434

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.

Affected products

• Mozilla Firefox: before 140.0 — fixed in 140.0
• Mozilla Thunderbird: before 140.0 — fixed in 140.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 140.0; Mozilla Thunderbird 140.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1950056
• https://bugzilla.mozilla.org/show_bug.cgi?id=1961777
• https://www.mozilla.org/security/advisories/mfsa2025-51/
• https://www.mozilla.org/security/advisories/mfsa2025-54/

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