ShadowPad backdoor was spread in corporate networks through software update mechanism

Pierluigi Paganini August 16, 2017

Kaspersky Lab discovered attackers were able to modify the NetSarang software update process to include a malware tracked as ShadowPad backdoor.

Software update mechanism could be an efficient attack vector, news of the day is that hackers compromised the update process for a popular server management software package developed by NetSarang.

Attackers were able to modify the software update process last month and modified it to include a backdoor tracked as ShadowPad, that affected at least one victim’s machine in Hong Kong.

NetSarang Computer, Inc. provides secure connectivity solutions and specializes in the development of server management tools for large corporate networks in many industries, including financial services, energy, retail, technology, and media.

In July, researchers at Kaspersky Lab were investigating suspicious DNS requests in a partner’s network. The requests were found on systems used to process transactions in a customer’s network in the financial industry.

Further investigation into the DNS queries led them to NetSarang, that promptly sanitized its software update process by removing the malicious library nssock2.dll in its update package,

“In July 2017, during an investigation, suspicious DNS requests were identified in a partner’s network. The partner, which is a financial institution, discovered the requests originating on systems involved in the processing of financial transactions.” states the analysis published by Kaspersky.

“Further investigation showed that the source of the suspicious DNS queries was a software package produced by NetSarang.”

Attackers have surreptitiously modified the software distributed by NetSarang to include an encrypted payload that could be remotely activated.

The attackers leveraged several layers of encrypted code to hide their ShadowPad backdoor and activate it only through the receiving of a special packet from the first tier command and control (C&C) server (“activation C&C server”).

“Activation of the payload would be triggered via a specially crafted DNS TXT record for a specific domain. The domain name is generated based on the current month and year values, e.g. for August 2017 the domain name used would be “”.” continues the analysis.

The module sends back to the C&C DNS  server basic target information (domain and user name, system date, network configuration) and in turn receives back the decryption key for the next stage of the code, activating the ShadowPad backdoor.

The data exchanged between the module and the C&C server is encrypted with a proprietary algorithm, experts noticed that each packet also contains an encrypted “magic” DWORD value “52 4F 4F 44” (‘DOOR’ if read as a little-endian value).

ShadowPad backdoor software update process

The ShadowPad backdoor is a modular platform that can be used to download and execute arbitrary code on the infected system, create processes, and maintain a virtual file system in the registry,

The remote access capability implemented for the ShadowPad backdoor includes a domain generation algorithm (DGA) for C&C servers which changes every month. Expert noticed that the thread actor behind the ShadowPad backdoor have already registered the domains covering July to December 2017, a circumstance that led them to believe that the start date of the attack is around mid-July 2017.

Kaspersky Lab revealed that the first known compile date for the ShadowPad backdoor is Jul 13, hackers signed the malicious code with a legitimate NetSarang certificate.

ShadowPad is an example of the dangers posed by an attack against software update process, recently other successful supply-chain attacks made the headlines such as the NotPetya that was spread through exploiting the software supply chain of the Ukrainian financial software provider MeDoc.

NetSarang customers urge to check their software to check the presence the backdoor. The affected versions of NetSarang containing the malicious nssock2.dll are Xmanager Enterprise 5 Build 1232, Xmanager 5 Build 1045, Xshell 5 Build 1322, Xftp 5 Build 1218 and Xlpd 5 Build 1220.

“Given that the NetSarang programs are used in hundreds of critical networks around the world, on servers and workstations belonging to system administrators, it is strongly recommended that companies take immediate action to identify and contain the compromised software,” states Kaspersky Lab.

Kaspersky published the list of Indicators of Compromise to help companies to check their systems.

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Pierluigi Paganini

(Security Affairs – ShadowPad backdoor, supply chain)

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