CVE-2025-52691 SmarterTools SmarterMail: dangerous file upload
In plain words: The program accepts files it should refuse, such as programs disguised as ordinary uploads. The attacker can place and run their own tools on the server.
Confirmed exploited by CISA on · US federal patch deadline Feb 16, 2026
What to do
- Install SmarterTools's security update for SmarterMail. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Keep a list of every internet-facing server you run so nothing is forgotten.
- Patch anything in this catalog first, ahead of normal patch cycles.
- Put admin and file-transfer apps behind a VPN or single sign-on instead of the open internet.
Who is affected
Work IT. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.
What's at risk: Mass data theft and ransomware: a single flaw in a file-transfer or email server has exposed thousands of organisations at once.
The details
- Official name
- SmarterTools SmarterMail Unrestricted Upload of File with Dangerous Type Vulnerability
- Product
- SmarterTools SmarterMail
- CISA description
- SmarterTools SmarterMail contains an unrestricted upload of file with dangerous type vulnerability that could allow an unauthenticated attacker to upload arbitrary files to any location on the mail server, potentially enabling remote code execution.
- Type of flaw
- Dangerous file upload (CWE-434)
- Confirmed exploited
- Jan 26, 2026 — known to be used in ransomware attacks
- US federal patch deadline
- Feb 16, 2026
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Answering about CVE-2025-52691 ·
Questions about CVE-2025-52691
Is CVE-2025-52691 being exploited?
Yes. CISA added CVE-2025-52691 to its Known Exploited Vulnerabilities catalog on Jan 26, 2026, which means there is reliable evidence of real-world attacks, including by ransomware groups.
How do I fix CVE-2025-52691?
Install SmarterTools's security update for SmarterMail. If no update exists, follow the vendor's workaround or stop using the product until one ships. Keep a list of every internet-facing server you run so nothing is forgotten.
Am I affected by CVE-2025-52691?
Only if you use SmarterTools SmarterMail. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.