CVE-2021-25667

Unauthenticated service interruption via malformed STP BPDU

Published Mar 15, 2021 · Updated Jun 2, 2026

Stack-based buffer overflow in Siemens SCALANCE and RUGGEDCOM firmware allows remote attackers to interrupt service via crafted STP BPDU frames. The BPDU-processing path writes frame data beyond a stack buffer while handling Spanning Tree Protocol traffic. Exploitation requires Layer 2 reachability and an active passive-listening feature; the grounded consequence is service interruption.

CVSS severity8.8
High
EPSS probability0.86%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack-based buffer overflow in Siemens SCALANCE and RUGGEDCOM firmware allows remote attackers to interrupt service via crafted STP BPDU frames. The BPDU-processing path writes frame data beyond a stack buffer while handling Spanning Tree Protocol traffic. Exploitation requires Layer 2 reachability and an active passive-listening feature; the grounded consequence is service interruption.

The record

CVE
CVE-2021-25667
Published
Mar 15, 2021
Updated
Jun 2, 2026
Vendor
Siemens
Product
SCALANCE XC-200
Classifications
CWE-787, CWE-121, T1499
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Jun 2, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=All versions < V4.1

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Siemens · SCALANCE XC-200version=All versions < V4.1
Siemens · SCALANCE S615version=All versions >= V4.3 and < V6.4
Siemens · SCALANCE XR500version=All versions < V6.2
Siemens · SCALANCE XM400version=All versions < V6.2
Siemens · SCALANCE XP-200version=All versions < V4.1
Siemens · SCALANCE XB-200version=All versions < V4.1
Siemens · SCALANCE XF-200BAversion=All versions < V4.1
Siemens · RUGGEDCOM RM1224version=All versions >= V4.3 and < V6.4
Siemens · SCALANCE XR-300WGversion=All versions < V4.1
Siemens · SCALANCE SC-600 Familyversion=All versions >= V2.0 and < V2.1.3
Siemens · SCALANCE M-800version=All versions >= V4.3 and < V6.4

Published CVSS scores

8.8Siemens ProductCERTCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
6.5CISA-ADPCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
CWE-121Stack-based Buffer Overflow
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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