VulnerabilityPublished 12 Mar 2026Updated 13 Mar 2026

CVE-2026-25823: Stack-based Buffer Overflow

Source CVE Database V5

Not known to be exploited · CVSS 9.8 Critical.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

9.8Critical

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.7% chance of exploitation in 30 days – higher than 54% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 12 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

AI-suggested

Immediate network segmentation: Isolate Ewon Flexy and Cosy+ devices from general IT networks and restrict access to trusted management networks only.
Implement strict firewall rules and access control lists (ACLs) to block unauthorized inbound traffic to these devices, especially from untrusted external sources.
Monitor network traffic for unusual activity targeting these devices, including attempts to exploit buffer overflow conditions.
Regularly check for and apply firmware updates from HMS Networks as soon as patches addressing CVE-2026-25823 are released.
Employ intrusion detection/prevention systems (IDS/IPS) tuned to detect exploitation attempts of stack buffer overflows and anomalous device behavior.
Conduct security audits and vulnerability assessments focused on OT environments to identify and remediate exposure points.
Limit physical and remote access to these devices to authorized personnel only, using multi-factor authentication where possible.
Maintain up-to-date asset inventories to quickly identify affected devices and prioritize remediation efforts. These steps go beyond generic advice by emphasizing network architecture changes, active monitoring, and operational security controls tailored to industrial environments.

Description

CVE-2026-25823 is a critical stack buffer overflow vulnerability affecting HMS Networks Ewon Flexy and Cosy+ devices with certain firmware versions prior to 15.0s4, 22.1s6, and 23.0s3 respectively. This vulnerability allows unauthenticated remote attackers to cause a denial of service or potentially achieve remote code execution. The flaw arises from improper handling of input leading to stack corruption (CWE-121). Exploitation requires no authentication or user interaction and can compromise confidentiality, integrity, and availability of the affected devices. No public exploits are currently known, but the high CVSS score of 9.8 reflects the severe risk. Organizations using these industrial communication devices should prioritize firmware updates once patches become available and implement network segmentation to reduce exposure.

Impact

The impact of CVE-2026-25823 is significant for organizations relying on HMS Networks Ewon Flexy and Cosy+ devices, which are commonly deployed in industrial automation, manufacturing, and critical infrastructure sectors. Successful exploitation can lead to complete device compromise, allowing attackers to disrupt operational technology (OT) environments by causing denial of service or executing arbitrary commands remotely. This can result in operational downtime, loss of control over industrial processes, data breaches, and potential safety hazards. The unauthenticated nature of the exploit increases the risk of widespread attacks, especially if devices are exposed to untrusted networks or the internet. Additionally, attackers could leverage compromised devices as footholds for further network intrusion, threatening broader enterprise IT and OT environments. The critical severity and ease of exploitation necessitate urgent attention to prevent potential large-scale disruptions and financial losses.

CWE-121Stack-based Buffer Overflow (opens in a new tab)
Variant weaknessLikelihood of exploit: HighCWE Top 25 (2025): #14
A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).
Operation · Build and Compilation · Environment Hardening
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index…
Architecture and Design
Use an abstraction library to abstract away risky APIs. Not a complete solution.
Implementation
Implement and perform bounds checking on input.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 20 Mar 2026, 02:34 UTC

WeaknessesCWE-121

Technical details

References

Community reviews

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