CVE-2021-20703Network attack vector

Unauthenticated code execution via Transaction Server overflow

Published Nov 2, 2021 · Updated Aug 3, 2024

Stack-based buffer overflow in NEC EXPRESSCLUSTER X 4.3 and earlier for Windows allows remote attackers to execute arbitrary code. The clptrnsv.exe service overflows a stack buffer while processing opcode 0x32 and initializing a clpexescript routine from crafted protocol data. No authentication or user interaction is required; access to the Transaction Server protocol on TCP port 29002 permits execution with SYSTEM privileges.

CVSS severity9.8
Critical
EPSS probability2.14%
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 NEC EXPRESSCLUSTER X 4.3 and earlier for Windows allows remote attackers to execute arbitrary code. The clptrnsv.exe service overflows a stack buffer while processing opcode 0x32 and initializing a clpexescript routine from crafted protocol data. No authentication or user interaction is required; access to the Transaction Server protocol on TCP port 29002 permits execution with SYSTEM privileges.

The record

CVE
CVE-2021-20703
Published
Nov 2, 2021
Updated
Aug 3, 2024
Vendor
NEC Corporation
Product
EXPRESSCLUSTER X
Classifications
CWE-120, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 2, 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=CLUSTERPRO X 4.3 for Windows and earlier, EXPRESSCLUSTER X 4.3 for Windows and earlier, CLUSTERPRO X 4.3 SingleServerSafe for Windows and earlier, EXPRESSCLUSTER X 4.3 SingleServerSafe for Windows and earlier

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NEC Corporation · EXPRESSCLUSTER Xversion=CLUSTERPRO X 4.3 for Windows and earlier, EXPRESSCLUSTER X 4.3 for Windows and earlier, CLUSTERPRO X 4.3 SingleServerSafe for Windows and earlier, EXPRESSCLUSTER X 4.3 SingleServerSafe for Windows and earlier

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.

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')
T1190Exploit Public-Facing Application

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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