CVE-2021-31886Public exploitNetwork attack vector

Remote code execution via oversized FTP username

Published Nov 9, 2021 · Updated Aug 3, 2024

Stack-based buffer overflow in Siemens Nucleus NET allows remote attackers to execute code or crash affected devices through FTP. The FTP server fails to validate the USER argument length before copying the supplied username into a stack buffer. Network access to an enabled FTP service is sufficient; Desigo products ship with FTP disabled by default.

CVSS severity9.8
Critical
EPSS probability3.05%
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 Nucleus NET allows remote attackers to execute code or crash affected devices through FTP. The FTP server fails to validate the USER argument length before copying the supplied username into a stack buffer. Network access to an enabled FTP service is sufficient; Desigo products ship with FTP disabled by default.

The record

CVE
CVE-2021-31886
Published
Nov 9, 2021
Updated
Aug 3, 2024
Vendor
Siemens
Product
TALON TC Compact (BACnet)
Classifications
CWE-170, T1190, T0866
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 9, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=All versions < V3.5.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Siemens · TALON TC Compact (BACnet)version=All versions < V3.5.4
Siemens · APOGEE PXC Modular (P2 Ethernet)version=All versions < V2.8.19
Siemens · Desigo PXC00-Uversion=All versions >= V2.3 and < V6.30.016
Siemens · Desigo PXC100-E.Dversion=All versions >= V2.3 and < V6.30.016
Siemens · APOGEE MBC (PPC) (BACnet)version=All versions
Siemens · Desigo PXC22-E.Dversion=All versions >= V2.3 and < V6.30.016
Siemens · APOGEE MEC (PPC) (BACnet)version=All versions
Siemens · Desigo PXM20-Eversion=All versions >= V2.3 and < V6.30.016
Siemens · Nucleus Source Codeversion=All versions
Siemens · Desigo PXC22.1-E.Dversion=All versions >= V2.3 and < V6.30.016
Siemens · Nucleus NET for Nucleus PLUSversion=All versions
Siemens · APOGEE MEC (PPC) (P2 Ethernet)version=All versions
Siemens · Nucleus ReadyStart V3version=All versions < V2017.02.4
Siemens · APOGEE PXC Compact (BACnet)version=All versions < V3.5.4
Siemens · TALON TC Modular (BACnet)version=All versions < V3.5.4
Siemens · Desigo PXC64-Uversion=All versions >= V2.3 and < V6.30.016
Siemens · APOGEE MBC (PPC) (P2 Ethernet)version=All versions
Siemens · Desigo PXC50-E.Dversion=All versions >= V2.3 and < V6.30.016
Siemens · Desigo PXC12-E.Dversion=All versions >= V2.3 and < V6.30.016
Siemens · Desigo PXC36.1-E.Dversion=All versions >= V2.3 and < V6.30.016
Siemens · APOGEE PXC Modular (BACnet)version=All versions < V3.5.4
Siemens · APOGEE PXC Compact (P2 Ethernet)version=All versions < V2.8.19
Siemens · Desigo PXC00-E.Dversion=All versions >= V2.3 and < V6.30.016
Siemens · Desigo PXC001-E.Dversion=All versions >= V2.3 and < V6.30.016
Siemens · Desigo PXC128-Uversion=All versions >= V2.3 and < V6.30.016
Siemens · Desigo PXC200-E.Dversion=All versions >= V2.3 and < V6.30.016

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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.

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No observations available

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

Weakness, pattern, technique

CWE-170Improper Null Termination
T1190Exploit Public-Facing Application
T0866Exploitation of Remote Services

Public exploit references

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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