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VulnerabilityPublished Updated

CVE-2025-6435: Mozilla Firefox · Unrestricted File Upload

Affects Mozilla FirefoxSource CVE Database V5

0

Not known to be exploited · CVSS 8.1 High : upgrade to 140 soon.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score
8.1High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 39% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 140
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 24 Jun 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade Mozilla Firefox to 140.

Affected software

ProductAffectedFixed in
Mozilla FirefoxAffected
  • <140
Fixed in
  • 140

AI-suggested

Mozilla has released an official fix for this vulnerability in Firefox 140. Users and administrators should update to Firefox 140 or later to remediate this issue. No additional mitigation steps are required beyond applying the official update.

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.

References

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