CVE-2021-33719Network attack vector

Unauthenticated code execution via TCP buffer overflow

Published Sep 14, 2021 · Updated Aug 3, 2024

Buffer overflow in Siemens SIPROTEC 5 relay firmware before 8.80 allows remote attackers to execute code or interrupt service via TCP port 4443. Packet processing on port 4443 copies attacker-controlled data without checking that it fits the destination buffer; Siemens does not disclose the affected function. No authentication or user interaction is required; service interruption is established, while code execution requires circumstances that Siemens does not disclose.

CVSS severity9.8
Critical
EPSS probability2.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Siemens SIPROTEC 5 relay firmware before 8.80 allows remote attackers to execute code or interrupt service via TCP port 4443. Packet processing on port 4443 copies attacker-controlled data without checking that it fits the destination buffer; Siemens does not disclose the affected function. No authentication or user interaction is required; service interruption is established, while code execution requires circumstances that Siemens does not disclose.

The record

CVE
CVE-2021-33719
Published
Sep 14, 2021
Updated
Aug 3, 2024
Vendor
Siemens
Product
SIPROTEC 5 relays with CPU variant CP100
Classifications
CWE-120, T0814
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 14, 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

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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 < V8.80

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Siemens · SIPROTEC 5 relays with CPU variant CP100version=All versions < V8.80
Siemens · SIPROTEC 5 relays with CPU variant CP050version=All versions < V8.80
Siemens · SIPROTEC 5 relays with CPU variant CP300version=All versions < V8.80

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T0814Denial 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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