CVE-2017-20203Known exploitationNetwork attack vector

Remote code execution via DNS-triggered malicious library

Published Oct 9, 2025 · Updated Nov 21, 2025

Embedded malicious code in NetSarang 5.0 products allows remote attackers to execute code through a DNS-triggered backdoor. The nssock2.dll library beacons to a month-derived domain, accepts a decryption key in a crafted DNS TXT response, and then runs downloaded code while maintaining an encrypted registry VFS. Execution requires an affected package to be installed and the backdoor to receive its C2 trigger; before activation it still discloses host, domain, user, date, and network details.

CVSS severity9.3
Critical
EPSS probability0.67%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Embedded malicious code in NetSarang 5.0 products allows remote attackers to execute code through a DNS-triggered backdoor. The nssock2.dll library beacons to a month-derived domain, accepts a decryption key in a crafted DNS TXT response, and then runs downloaded code while maintaining an encrypted registry VFS. Execution requires an affected package to be installed and the backdoor to receive its C2 trigger; before activation it still discloses host, domain, user, date, and network details.

The record

CVE
CVE-2017-20203
Published
Oct 9, 2025
Updated
Nov 21, 2025
Vendor
NetSarang Computer, Inc.
Product
Xshell
Classifications
CWE-506, T1071.004, T1195.002, T1112, T1105
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 1, 2017Exploitation reportedActivated ShadowPad deployment in Hong Kong
  2. Oct 9, 2025CVE publishedPublication date reported by the CVE source.
  3. Nov 21, 2025Record 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=5.0 Build 1322

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NetSarang Computer, Inc. · Xshellversion=5.0 Build 1322
NetSarang Computer, Inc. · Xmanager Enterpriseversion=5.0 Build 1232
NetSarang Computer, Inc. · Xlpdversion=5.0 Build 1220
NetSarang Computer, Inc. · Xmanagerversion=5.0 Build 1045
NetSarang Computer, Inc. · Xftpversion=5.0 Build 1218

Published CVSS scores

9.3VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N

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 exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-506Embedded Malicious Code
T1071.004DNS
T1195.002Compromise Software Supply Chain
T1112Modify Registry
T1105Ingress Tool Transfer

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.

Reported exploitation

Technologies

Your stack

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Your stack

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