CVE-2026-25823

Critical

Published: 13 March 2026

Published

13 March 2026

Modified

27 April 2026

KEV Added

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Patch

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CVSS Score v3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0073 49.3th percentile

Risk Priority 70 floored blend · peak EPSS

Summary

CVE-2026-25823 is a critical-severity Stack-based Buffer Overflow (CWE-121) vulnerability in Windows (inferred from references). Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 49.3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

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

Deeper analysis

CVE-2026-25823 is a stack buffer overflow vulnerability (CWE-121) in HMS Networks' Ewon Flexy and Cosy+ devices. It affects Ewon Flexy with firmware before version 15.0s4, Cosy+ with firmware 22.xx before 22.1s6, and Cosy+ with firmware 23.xx before 23.0s3. The issue enables denial of service and can be further exploited for unauthenticated remote code execution, earning a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

Remote attackers require no privileges or user interaction to exploit the vulnerability over the network with low complexity. Exploitation can crash affected devices, causing denial of service, or achieve remote code execution, resulting in high impacts to confidentiality, integrity, and availability.

HMS Networks has published a security advisory detailing this and related vulnerabilities in Ewon Flexy and Cosy+ devices, available at https://hmsnetworks.blob.core.windows.net/nlw/docs/default-source/products/cybersecurity/security-advisory/hms-security-advisory-2026-03-09-001---ewon-several-flexy-and-cosy--vulnerabilities.pdf?sfvrsn=f7c027b8_13. Mitigation involves updating to the specified firmware versions: 15.0s4 for Ewon Flexy, 22.1s6 for Cosy+ 22.xx, and 23.0s3 for Cosy+ 23.xx. Additional product information is at https://www.hms-networks.com/p/flexy20500-00ma-ewon-flexy-205.

EU & UK References

🇪🇺 ENISA EUVD: EUVD-2026-11715

Vulnerability details

HMS Networks Ewon Flexy with firmware before 15.0s4, Cosy+ with firmware 22.xx before 22.1s6, and Cosy+ with firmware 23.xx before 23.0s3 have a stack buffer overflow that leads to a Denial of Service, which can also be exploited to achieve…

Unauthenticated Remote Code Execution.

CWE(s): CWE-121

Related Threats

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?

Stack buffer overflow vulnerability in public-facing HMS Networks Ewon Flexy and Cosy+ devices allows unauthenticated remote code execution over the network, directly enabling T1190: Exploit Public-Facing Application.

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