CVE-2025-52691

CriticalCISA KEVActive ExploitationPublic PoCRansomware-linked

Published: 29 December 2025

Published

29 December 2025

Modified

27 January 2026

KEV Added

26 January 2026

Patch

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CVSS Score 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS Score 0.8738 99.5th percentile

Risk Priority 92 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2025-52691 is a critical-severity Unrestricted Upload of File with Dangerous Type (CWE-434) vulnerability in Smartertools Smartermail. Its CVSS base score is 10.0 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 0.5% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190). What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Directly mandates timely identification, reporting, and patching of critical flaws like this unrestricted file upload vulnerability in SmarterMail to prevent exploitation.

SI-10 Information Input Validation good match

prevent

Requires information input validation at upload points to restrict dangerous file types and arbitrary placements, directly countering CWE-434 unrestricted uploads.

SI-3 Malicious Code Protection partial match

preventdetect

Deploys malicious code protection mechanisms to scan for and block execution of arbitrarily uploaded files leading to remote code execution.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

Why these techniques?

Unauthenticated arbitrary file upload to any location on public-facing SmarterMail mail server enables remote code execution, directly mapping to T1190: Exploit Public-Facing Application.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

NVD Description

Successful exploitation of the vulnerability could allow an unauthenticated attacker to upload arbitrary files to any location on the mail server, potentially enabling remote code execution.

Deeper analysisAI

CVE-2025-52691 is a critical vulnerability (CVSS 10.0, CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H) affecting SmarterMail, a mail server software. It stems from CWE-434 (Unrestricted Upload of File with Dangerous Type), where successful exploitation allows an unauthenticated attacker to upload arbitrary files to any location on the server, potentially leading to remote code execution. The vulnerability was published on 2025-12-29.

An unauthenticated attacker with network access can exploit this vulnerability with low complexity and no user interaction required. By uploading malicious files to arbitrary server locations, the attacker can achieve high confidentiality, integrity, and availability impacts, including full remote code execution in a scoped manner.

Advisories from the Cyber Security Agency of Singapore (CSA) at https://www.csa.gov.sg/alerts-and-advisories/alerts/al-2025-124/, WatchTowr Labs GitHub analysis at https://github.com/watchtowrlabs/watchTowr-vs-SmarterMail-CVE-2025-52691?ref=labs.watchtowr.com, and CISA's Known Exploited Vulnerabilities Catalog at https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-52691 provide further details on exploitation and mitigation recommendations.

This vulnerability is listed in CISA's Known Exploited Vulnerabilities Catalog, indicating active real-world exploitation.