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Mozilla CVE-2025-6435

| EUVDEUVD-2025-19016 HIGH
Unrestricted Upload of File with Dangerous Type (CWE-434)
2025-06-24 security@mozilla.org
Mozilla File Upload
High
Disputed · 8.1 NVD
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Severity by source

Sources disagree (Low–High)
NVD PRIMARY
8.1 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Ubuntu
MEDIUM
qualitative
SUSE
HIGH
qualitative
Red Hat
3.4 LOW
qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

4
Patch released
Mar 31, 2026 - 21:13 nvd
Patch available
EUVD ID Assigned
Mar 15, 2026 - 22:36 euvd
EUVD-2025-19016
Analysis Generated
Mar 15, 2026 - 22:36 vuln.today
CVE Published
Jun 24, 2025 - 13:15 nvd
HIGH 8.1

DescriptionCVE.org

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 affects Firefox < 140 and Thunderbird < 140.

AnalysisAI

CVE-2025-6435 is a file handling vulnerability in Firefox and Thunderbird's Developer Tools where saved network responses may lack the .download file extension, potentially allowing attackers to trick users into executing malicious executables. This affects Firefox versions below 140 and Thunderbird versions below 140. The vulnerability requires user interaction (saving and executing a file) but carries high severity (CVSS 8.1) due to potential for arbitrary code execution.

Technical ContextAI

The vulnerability exists in the Network tab of Firefox/Thunderbird Developer Tools (DevTools), specifically in the 'Save As' context menu functionality. When a user right-clicks on a network response and selects 'Save As', the file handling mechanism fails to properly append or enforce the .download file extension. This relates to CWE-434 (Unrestricted Upload of File with Dangerous Type), which encompasses improper validation of file types and extensions during file operations. The root cause is insufficient file extension validation in the save dialog handler. The affected CPE would be cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* (versions <140) and cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* (versions <140). The issue affects the DevTools frontend code responsible for exporting/saving HTTP responses.

RemediationAI

Patch/Update: Upgrade Firefox to version 140 or later (Mozilla) Patch/Update: Upgrade Thunderbird to version 140 or later (Mozilla) Workaround: Until patched, avoid using 'Save As' on network responses in DevTools for potentially untrusted network traffic. Manually verify file extensions before execution. (User) Mitigation: Implement application whitelisting and file execution policies to prevent execution of files saved from untrusted sources without proper validation. (Organizational) Mitigation: Configure browser to treat downloaded/saved files as requiring explicit confirmation before execution. (OS/browser)

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Same weakness CWE-434 – Unrestricted Upload of File with Dangerous Type

View all
CVE-2016-3088 CRITICAL POC
9.8
CVE-2021-31207 MEDIUM POC
6.6
CVE-2017-12617 HIGH POC
8.1
CVE-2017-11357 CRITICAL POC
9.8
CVE-2017-12615 HIGH POC
8.1
CVE-2024-5084 CRITICAL POC
9.8
CVE-2020-36847 CRITICAL POC
9.8
CVE-2017-6090 HIGH POC
8.8

Same technique File Upload

View all
CVE-2016-3088 CRITICAL POC
9.8
CVE-2017-12617 HIGH POC
8.1
CVE-2017-11357 CRITICAL POC
9.8
CVE-2017-12615 HIGH POC
8.1
CVE-2024-5084 CRITICAL POC
9.8
CVE-2016-6600 CRITICAL POC
9.8
CVE-2017-6090 HIGH POC
8.8
CVE-2015-8249 CRITICAL POC
9.8

Vendor StatusVendor

Ubuntu

Priority: Medium
firefox
Release Status Version
jammy not-affected code not present
noble not-affected code not present
oracular not-affected code not present
plucky not-affected code not present
upstream needs-triage -
questing not-affected code not present
thunderbird
Release Status Version
noble not-affected code not present
oracular not-affected code not present
plucky not-affected code not present
upstream released 140
jammy released 1:140.7.1+build1-0ubuntu0.22.04.1
questing not-affected code not present
mozjs38
Release Status Version
bionic needs-triage -
jammy DNE -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs52
Release Status Version
bionic ignored -
focal ignored -
jammy DNE -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs68
Release Status Version
focal ignored -
jammy DNE -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs78
Release Status Version
jammy ignored -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs91
Release Status Version
jammy ignored -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs102
Release Status Version
jammy ignored -
noble ignored -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs115
Release Status Version
jammy DNE -
noble ignored -
oracular ignored -
plucky ignored -
upstream needs-triage -
questing DNE -
USN-7991-1

Debian

firefox
Release Status Fixed Version Urgency
sid fixed 148.0.2-1 -
(unstable) fixed 140.0-1 -

SUSE

Severity: High
Product Status
Image SLES12-SP5-SAP-Azure-LI-BYOS-Production Image SLES12-SP5-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP4-SAP-Azure-LI-BYOS Image SLES15-SP4-SAP-Azure-LI-BYOS-Production Image SLES15-SP4-SAP-Azure-VLI-BYOS Image SLES15-SP4-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP5-SAP-Azure-LI-BYOS Image SLES15-SP5-SAP-Azure-LI-BYOS-Production Image SLES15-SP5-SAP-Azure-VLI-BYOS Image SLES15-SP5-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP6-SAP-Azure-LI-BYOS Image SLES15-SP6-SAP-Azure-LI-BYOS-Production Image SLES15-SP6-SAP-Azure-VLI-BYOS Image SLES15-SP6-SAP-Azure-VLI-BYOS-Production Image SLES15-SP7-SAP-Azure-LI-BYOS-Production Image SLES15-SP7-SAP-Azure-VLI-BYOS-Production Affected
SUSE Enterprise Storage 7.1 Fixed

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CVE-2025-6435 vulnerability details – vuln.today
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