CVE-2017-20203
Published: 09 October 2025
Summary
CVE-2017-20203 is a critical-severity Embedded Malicious Code (CWE-506) vulnerability in Securelist (inferred from references). Its CVSS base score is 9.3 (Critical).
Operationally, ranked in the top 23.9% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2017-18919
Vulnerability details
NetSarang Xmanager Enterprise 5.0 Build 1232, Xmanager 5.0 Build 1045, Xshell 5.0 Build 1322, Xftp 5.0 Build 1218, and Xlpd 5.0 Build 1220 contain a malicious nssock2.dll that implements a multi-stage, DNS-based backdoor. The dormant library contacts a C2 DNS…
more
server via a specially crafted TXT record for a month‑generated domain. After receiving a decryption key, it then downloads and executes arbitrary code, creates an encrypted virtual file system (VFS) in the registry, and grants the attacker full remote code execution, data exfiltration, and persistence. NetSarang released builds for each product line that remediated the compromise: Xmanager Enterprise Build 1236, Xmanager Build 1049, Xshell Build 1326, Xftp Build 1222, and Xlpd Build 1224. Kaspersky Lab identified an instance of exploitation in the wild in August 2017.
- CWE(s)
Related Threats
No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Restricting software to licensed versions and controlling P2P prevents introduction of software containing embedded malicious code from unauthorized sources.
The control prevents users from installing software that contains embedded malicious code.
Regular inventory reviews and updates make it harder to conceal or exploit embedded malicious code by requiring all components to be documented and accounted for.
Reverting to a known state removes any malicious code embedded by an attacker.
The approval and review process for maintenance tools can prevent introduction or continued use of tools containing embedded malicious code.
Supply chain strategy requires vetting and controls during acquisition to prevent or detect insertion of malicious code by vendors or integrators.
Background screening for development or deployment roles makes intentional insertion of malicious code by insiders materially harder to accomplish.
The capability explicitly searches for embedded malicious code and backdoors as indicators of compromise.