Malicious file execution via unsanitized Save As extension
Published Jun 24, 2025 · Updated Apr 13, 2026
Dangerous file handling in Mozilla Firefox and Thunderbird before 140 allows remote attackers to induce malicious file execution. The DevTools Save Response As helper preserves dangerous response-derived extensions instead of appending .download, allowing files such as .url or .lnk to retain executable behavior. Exploitation requires a user to open DevTools, save a malicious response from the Network tab, and then execute the resulting local file.
Summary
What happened
Dangerous file handling in Mozilla Firefox and Thunderbird before 140 allows remote attackers to induce malicious file execution. The DevTools Save Response As helper preserves dangerous response-derived extensions instead of appending .download, allowing files such as .url or .lnk to retain executable behavior. Exploitation requires a user to open DevTools, save a malicious response from the Network tab, and then execute the resulting local file.
The record
- CVE
- CVE-2025-6435
- Published
- Jun 24, 2025
- Updated
- Apr 13, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-434, T1204.002
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 24, 2025CVE publishedPublication date reported by the CVE source.
- Apr 13, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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What conditions does exploitation require?
What is affected?
Affected products and versions are unavailable in this record.
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- DevTools Save Response As proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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