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Stack-based Buffer OverflowWeakness · CWE-121

CVE-2026-25823

CRITICAL · 9.8 CVSS v3.1 Published 2026-03-13
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A stack buffer overflow vulnerability in HMS Networks Ewon Flexy and Cosy+ devices allows attackers to cause Denial of Service and achieve Unauthenticated Remote Code Execution. The vulnerability affects specific firmware versions across three product lines (Flexy <15.0s4, Cosy+ 22.xx <22.1s6, Cosy+ 23.xx <23.0s3).

MitigationUpgrade affected devices to the specified firmware versions (15.0s4, 22.1s6, or 23.0s3) to remediate the vulnerability. If immediate patching is not possible, isolate these devices behind a firewall or VLAN to reduce exposure.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the Ewon device model
    Access the device web interface or CLI and locate the product name/model information. Look for "Flexy" or "Cosy+" designation in the device info or label.
    Affected if The device is not an Ewon Flexy or Cosy+ product, this CVE does not apply.
  2. Determine the firmware version
    Log into the device web interface (typically https://<device_ip>/) and navigate to System > Status or About section. Alternatively, access via SSH or serial console and run the command to display firmware version (often 'version' or 'sysinfo').
    Affected if Unable to retrieve the firmware version - manual inspection may be required.
  3. Compare Flexy firmware against affected range
    If the device is a Flexy, compare the installed firmware version to the affected range: any version below 15.0s4 (for example, 15.0s3, 14.x, 13.x, etc.) is vulnerable.
    Affected if Flexy firmware version is less than 15.0s4.
  4. Compare Cosy+ 22.xx firmware against affected range
    If the device is a Cosy+ with a 22.xx firmware branch (for example, 22.0s1, 22.1s0), compare to the affected threshold: any version below 22.1s6 is vulnerable.
    Affected if Cosy+ firmware version is 22.xx and less than 22.1s6.
  5. Compare Cosy+ 23.xx firmware against affected range
    If the device is a Cosy+ with a 23.xx firmware branch (for example, 23.0s0, 23.0s1), compare to the affected threshold: any version below 23.0s3 is vulnerable.
    Affected if Cosy+ firmware version is 23.xx and less than 23.0s3.

The device is affected if it is an Ewon Flexy with firmware below 15.0s4, or a Cosy+ with 22.xx firmware below 22.1s6, or a Cosy+ with 23.xx firmware below 23.0s3.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade affected devices to the specified firmware versions (15.0s4, 22.1s6, or 23.0s3) to remediate the vulnerability. If immediate patching is not possible, isolate these devices behind a firewall or VLAN to reduce exposure.

Recommended fix High confidence

Ewon Flexy: firmware 15.0s4 or later; Cosy+ 22.xx: firmware 22.1s6 or later; Cosy+ 23.xx: firmware 23.0s3 or later

  1. 1. Identify the HMS Networks device model (Ewon Flexy or Cosy+) and current firmware version
  2. 2. For Ewon Flexy devices: Navigate to the device web interface or use HMS firmware update tools
  3. 3. For Cosy+ devices: Determine if running 22.xx or 23.xx branch
  4. 4. Download the appropriate firmware update from HMS Networks official support channels
  5. 5. Apply firmware update: For Flexy, upgrade to 15.0s4 or later; For Cosy+ 22.xx, upgrade to 22.1s6 or later; For Cosy+ 23.xx, upgrade to 23.0s3 or later
  6. 6. After upgrade, verify the firmware version matches the fixed release
  7. 7. Confirm the device is operational and the vulnerability is remediated

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation6.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,960
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-25823 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data