CVE-2025-52691
CVE-2025-52691 is a security flaw in SmarterTools SmarterMail, mail server software. Attackers can run their own code on SmarterTools SmarterMail from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 26 Jan 2026, and says ransomware gangs have used it.[1]
SmarterTools SmarterMail is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. SmarterTools has published a fix or advice.
Description
CISA calls it an unrestricted upload of file with dangerous type in SmarterTools SmarterMail. In its words: “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.”[1]
The underlying weakness is unrestricted file upload (CWE-434), in MITRE’s list of common software weaknesses.[2]
It scores 10.0 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by the organisation that published the CVE using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; SmarterTools’s advisory has them[3]. CISA names the product as SmarterTools SmarterMail.
Most families won’t have SmarterTools SmarterMail; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 26 Jan 2026, 28 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 16 Feb 2026 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 86%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
SmarterTools has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]
- Check whether you use it.SmarterTools SmarterMail is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 16 Feb 2026 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 10.0.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 86%.[4] |
See also
Other SmarterTools SmarterMail flaws
- CVE-2026-24423: missing authentication for critical function ·
- CVE-2026-23760: authentication bypass using an alternate path or channel ·
Other unrestricted file upload flaws
- CVE-2026-48356, Adobe Commerce and Magento: unrestricted upload of file with dangerous type ·
- CVE-2026-56291, Balbooa Forms: unrestricted upload of file with dangerous type ·
- CVE-2026-48939, iCagenda: unrestricted upload of file with dangerous type ·
- CVE-2026-48908, JoomShaper SP Page Builder: unrestricted upload of file with dangerous type ·
- CVE-2024-7694, TeamT5 ThreatSonar Anti-Ransomware: unrestricted upload of file with dangerous type ·
Added the same day
- CVE-2026-24061, GNU InetUtils: argument injection ·
- CVE-2026-23760, SmarterTools SmarterMail: authentication bypass using an alternate path or channel ·
- CVE-2026-21509, Microsoft Office: security feature bypass ·
- CVE-2018-14634, Linux Kernel: integer overflow ·
Every SmarterTools flaw on CISA’s list · Everything added in January 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “SmarterTools SmarterMail Unrestricted Upload of File with Dangerous Type Vulnerability”. Known Exploited Vulnerabilities Catalog, added 26 Jan 2026.
- ^ National Institute of Standards and Technology. “CVE-2025-52691 Detail”. National Vulnerability Database, published 29 Dec 2025.
- ^ SmarterTools. Advisories and fixes: smartertools.com, csa.gov.sg.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.857, percentile 99.7, 31 Oct 2026.
- CVE Program. “CVE-2025-52691”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.