SectorA01 Custom Proxy Utility Tool Analysis


SectorA01 is one of the most infamous state sponsored threat actor groups globally and is unique in the sense that it is one of the only state sponsored groups with large interests in financial crime. So with the continued interest into SectorA01’s financial crime activities due to the recent potential misattribution of the Ryuk ransomware [1], we decided to perform an analysis into one of the tools – a proxy utility executable – used exclusively by SectorA01 that recently caught our attention again.

Interestingly, in the Hidden Cobra FASTCash report by the US-CERT [2] in October last year, there were two versions of a “Themida packed proxy service module” (i.e. x32 and x64 versions). Our analysis of those modules showed code reuse of critical functions with the sample we are analyzing in this post, leading us to think that those samples might be an evolution of this sample.

SectorA01 Proxy Utility

SectorA01 uses a variety of tools for different purposes, but one common custom tool used in the attacks targeting the Polish banks in 2016-2017 [3], a Taiwanese Bank in 2017 [4], and Vietnamese banks in 2018 [5] is one of their custom proxy utility executables.

The latest unique sample of this proxy utility we could find was on December 10th, 2018 from Canada. This leads us to one of a few possible theories that Canadian bank(s) may have been one of the many unreported or reported [6] targets during the time period of the attack on the Taiwanese bank based on the compilation timestamps.

As we can see from the FASTCash proxy samples below, at least one of their developers compiles the 64-bit sample immediately after compiling the 32-bit sample – behavior very normal for developers when compiling for multiple systems. The same thing can be seen for the two samples on 20 Feb 2017, and so in fact instead of calling them samples targeting a Taiwanese bank and potentially a Canadian bank, it may be more accurate to call it just one of the many pairs of 32-bit and 64-bit proxy samples produced by the group.

A proxy was also used against an unnamed Southeast Asian bank [7] which appears to be an older version of the proxy, and against an Indian bank [8] which appears to be a newer version of the proxy based our code analysis from samples in the US-CERT FASTCash report.

But despite the similarities, however, we are unable to definitively state that these samples were earlier (unnamed Southeast Asian bank) or later (FASTCash attack, such as against the Indian bank) versions of the proxy. After all, SectorA01 has more than one proxy tool in its arsenal, such as the proxy used together with their TYPEFRAME trojan [9] which has a separate code base.

DescriptionCompilation Timestamp
Attack on unnamed SEA bank (old version)17 Sep 2014 16:59:33
Attack on several Polish banks (variant)24 Aug 2015 10:21:52
Attack on Vietnamese banks (variant)2 May 2016 03:24:39
Attack on a Taiwanese Bank (32-bit) (variant)20 Feb 2017 11:09:30
Sample Discovered from Canada (64-bit) (sample analyzed)20 Feb 2017 11:09:41
FASTCash (32-bit) (new version)14 Aug 2017 17:14:04
FASTCash (64-bit) (new version)14 Aug 2017 17:14:12

Sample Background

This executable is a custom tunneling proxy utility tool in SectorA01’s toolkit. It can be used as either a tunneling proxy server to forward traffic to another destination, or as a tunneling proxy client which requests another infected tunneling proxy server to perform requests.

Besides being used as one of several ordinary proxy servers in a chain of servers to hide the source of attacks, against one example banking target from India in the FASTCash attacks, “a proxy server was created and transactions authorized by the fake or proxy server”. In this scenario, the proxy utility seems to be not used just as a secondary helper utility, but as the primary attack malware.

SectorA01 normally packs these samples with either the Themida or Enigma Protector, but in this blog post we will only be showing the analysis of the unpacked sample.

Process Arguments

This utility requires a single process argument in order for it to run. It attempts to decode the argument and only continues its execution path if the decoded argument match the format it is expecting.

The argument is delimited by the “|” symbol, and the utility decodes up to four tokens with each token being decoded individually. The first is required and used as the primary C2 server (malware acting as tunneling proxy server) or as the URL to be requested (malware acting as tunneling proxy client), the optional second token is used as the proxy target information, the optional third token is used as proxy server information, and the optional fourth token is an optional proxy username and password.

Each deobfuscated token is separated by a colon “:”, which is used as the deobfuscated process arguments delimiter.

int __stdcall WinMain_0(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd){ //deobfuscate process arguments here deobfuscation_complete: if ( strlen(deobfuscated_c2_1) != 0 && strchr(deobfuscated_c2_1, “:”) ){ … } return 0; }

The decoding algorithm makes use of a rotating character in an eight character string “cEzQfoPw” and the loop index to ensure that every deobfuscated character at a different index comes from a different two obfuscated characters.

We recreated this deobfuscation algorithm and created an obfuscation algorithm, which allowed us to forge our own process arguments. An example of a process argument which uses all four tokens could be “!y$t$A$s!z$S$e$U$Q$Y$1$W$U!}$d|!y#z$A$s!z$S$o$1$5$t$A$e$U!x|!y#{!}$Z$C$R$o$1$P#}$8$a!y!y|!00X!B0]0D!8#z$2$R0d$0$b!w!20c!70B0d”.

Example TokenDecoded C2 InformationUsage
!y$t$A$s!z$S$e$U$Q$Y$1$W$U!}$d Server (1-2 arguments)
Proxy Target (3-4 arguments)
!y#z$A$s!z$S$o$1$5$t$A$e$U!x172.16.1.1:443Proxy Target (2 arguments only)
!y#{!}$Z$C$R$o$1$P#}$8$a!y!y10.1.1.12:8080Proxy Server (3-4 arguments)
!00X!B0]0D!8#z$2$R0d$0$b!w!20c!70B0dsector%20a01:proxyProxy Authentication (4 arguments only)

Note that since the algorithm transforms every two encoded characters into one decoded character based on its character index, there are many possible two characters which will result in the same character, and finally countless different strings which would decode to a single string.

C2 Communication

The algorithm used for C2 communications is more straightforward – a combination of ADD/XOR repeatedly from each character in a hard coded 20 character byte array “{47 B0 62 0E 69 F3 22 8D 65 40 BF 39 24 A6 C3 BB 8E 68 EB B5}” is used for decoding, and the opposite XOR/SUB repeatedly from the reversed byte array is used for encoding. The algorithm restarts for each character without context, so it essentially ends up being a character substitution table.

There are eight commands to communicate with the C2 server, encoded by either the C2 server or the proxy client then decoded by the other side. These commands are in the Russian language but as other researchers have pointed out in the past, is simply a false flag.

In fact, in one of the analyzed malware used against an unnamed Southeast Asian bank, we see that what appears to be a much earlier versions of the proxy having seven numeric-only control codes while this sample has eight Russian language control codes, with the control codes in both samples having almost the same meaning.

OperationDescriptionHex Values over the Network
kliyent2podklyuchitMalware thread created notification (client)d1 14 23 b3 c7 b2 ac fe 70 0d 1c d1 14 b3 d7 f9 38 23 ac
NachaloClient has started (client)92 ab f9 38 ab 14 0d
ssylkaTunneling proxy server has started (client)c9 c9 b3 14 d1 ab
poluchitGet proxy target information (server)70 0d 14 d7 f9 38 23 ac
ustanavlivatSet proxy target information (server)d7 c9 ac ab b2 ab 2a 14 23 2a ab ac
pereslatStart a new tunneling proxy server session in new thread (server)70 c7 be c7 c9 14 ab ac
derzhatMaintain connection (server)1c c7 be b6 38 ab ac
vykhoditExit (server) / Client has exited (client)2a b3 d1 38 0d 1c 23 ac

Tunneling Proxy Server

When this utility acts as a tunneling proxy server, it directly uses Windows Sockets 2 (“WS2_32”) to achieve their rudimentary proxy.

signed __int64 __fastcall c2_ssylka(LPVOID lpThreadParameter){ SOCKET c2Socket = begin_c2(“ssylka”); … SOCKET targetProxySocket = retrieveProxySocket(); … start_tunnel_proxy_server(c2Socket, targetProxySocket); … } signed int __fastcall start_tunnel_proxy_server(SOCKET c2Socket, SOCKET targetProxySocket){ … numBytesReceived = recv(c2Socket, &dataToProxy, 0x2000, 0); … numBytesReceived = send(targetProxySocket, &dataToProxy, numBytesReceived, 0); … }

Tunneling Proxy Client

When this utility acts as a tunneling proxy client, it utilizes the more powerful embedded libcurl library (version 7.49.1 for this sample, but not always the case) to command other infected tunneling proxy servers.

__int64 __fastcall connect_to_proxy(__int64 fixedFunctionAddress, __int64 proxyTarget){ … curl_setopt(handle, CURLOPT_URL, proxyTarget); … curl_setopt(handle, CURLOPT_PROXY, fixedFunctionAddress + 16); //refers to deobfuscated proxy server information … curl_setopt(handle, CURLOPT_HTTPPROXYTUNNEL, 1); … if ( strlen((fixedFunctionAddress + 278)) != ) //if deobfuscated argument 4 is not empty curl_setopt(handle, CURLOPT_PROXYUSERPWD); //curl_setopt argument 3 = deobfuscated process argument 4, which is not detected by decompiler … } … }

The CURLOPT_HTTPPROXYTUNNEL code causes the client to starts by using HTTP CONNECT to the proxy server in order to request it to forward traffic to the proxy target.

>Internet Protocol Version 4, Src: x.x.x.x, Dst: >Transmission Control Protocol, Src Port: xxxxx, Dst Port: 8080, Seq: 1, Ack: 1, Len: 59 >Hypertext Transfer Protocol >CONNECT HTTP/1.1\r\n >[Expert Info (Chat/Sequence): CONNECT HTTP/1.1\r\n] Request Method: CONNECT Request URI: Request Version: HTTP/1.1 Host:\r\n

The FASTCash Connection

In October last year, the US-CERT reported about the “FASTCash” campaign by SectorA01, which was essentially an ATM cash-out scheme whereby SectorA01 remotely compromised bank payment switch applications to simultaneously physically withdraw from ATMs in many countries and steal millions of dollars.

Some of the artifacts used in the campaign included proxy modules, a RAT, and an installer application. When we performed a preliminary analysis and compared the FASTCash proxy module to the proxy module analyzed in this post, we found algorithmic similarities between the decoding/encoding functions, the process argument deobfuscation function, and the proxy function.

However, the FASTCash proxy module also had more functions in them with new capabilities as described briefly in the US-CERT FASTCash Malware Analysis Report [10]. Additionally, our own analysis showed that they have also updated the use of amateur-ish strings which were previously easily detectable from memory and obviously malicious, to now hiding or removing those custom strings. This is their normal behavior as it has been known that they are constantly modifying their own source code, and these similarities and developments leads us to think that the FASTCash proxy module might be an evolution of their previous proxy module.


Attribution is a complex and controversial topic, but regardless, correctly attributing a threat to a particular threat group is a far easier task than correctly attributing the threat to or being linked to a particular nation state. Given even a single piece of complex enough custom malware believed to be in possession by only a single group and context behind the attack, it is possible to have some degree of confidence of which group was behind the attack.

But even custom malware source code can get stolen, the executable itself repackaged, or the functions recreated. In a simpler scenario, false flags such as strings and metadata could also be placed.

Regarding the initial attribution of the Ryuk ransomware, however, while others have focused on the misattribution, our view is that even if it was correct it would simply have been a lucky guess. Basing attribution solely on the usage of a single privately purchasable malware is fundamentally flawed, and the simple truth is that no organization in the world would be able to track every piece of malware to know what is being sold in the dark and deep web anyway.

That is why in order to have a higher degree of confidence of who is behind an attack, the entirety of the threat’s tactics, techniques, and procedures (TTPs) need to be analyzed across multiple events using both trusted public and vetted private sources.

SectorA01 shows no signs of stopping their attacks against financial sectors worldwide and although they have been constantly modifying their code protectors, functions, and algorithms, there will be traces of similarities across different versions of their tools. Our Threat Recon Team will continue tracking such events and malware and report on our findings.

Unpacked Sample (SHA-256)


Memory Dump Samples from US-CERT FASTCash Report (SHA-256)



Packed Sample from Polish banks attack (SHA-256)


Sample from Taiwanese bank attack (SHA-256)


Sample from Vietnamese banks attack (SHA-256)


Attack on Unnamed SEA Bank (“TCP Tunnel Tool”) (SHA-256)



[1] Ryuk Ransomware Attack: Rush to Attribution Misses the Point
[2] HIDDEN COBRA – FASTCash Campaign
[3] Włamania do kilku banków skutkiem poważnego ataku na polski sektor finansowy
[5] High alert against malicious code attacks in Vietnam
[6] BMO and CIBC-owned Simplii Financial reveal hacks of customer data
[8] North Korean connection to Cosmos hacking? Signs point to Bangladesh heist masterminds
[9] MAR-10135536-12 – North Korean Trojan: TYPEFRAME
[10] MAR-10201537 – HIDDEN COBRA FASTCash-Related Malware

Monthly Threat Actor Groups Intelligence Report, December 2018

This is a summary of activity of suspected state sponsored Threat Actor Groups analyzed by the Threat Recon Team, based on data and information collected from November 21 to December 20, 2018.

1. SectorA Activity Features

A total of four hacking groups were found to be active within SectorA.

Among this detected activity, SectorA05 activity was relatively more intense than others and all SectorA05 activity was highly related to political hacking aimed at South Korea.

There are two main purposes of hacking by SectorA for the month, which can be distinguished by activity aimed at Korea and activity aimed at other countries.

The first is hacking activity targeting financial institutions overseas, and virtual currency exchanges and individual traders in South Korea. This is used to overcome financial and economic sanctions that are currently ongoing against SectorA. The second is hacking activity related to the more traditional espionage aimed at stealing information related to South Korea’s political and diplomatic activities.

Although malware and hacking techniques used by SectorA differ depending on the target, SectorA consistently targets individuals who belong to target organizations by utilizing Spear Phishing with malicious documents attached.

One of their strategies, using Cloud services as their C2 server for hacking activities, is used against both overseas and South Korean targets.

Another strategy, utilizing malware in the form of document reader files, differs depending on the target – overseas targets receive traditional Microsoft Office files, while South Korean targets will receive Hangeul Word Processor (HWP) files regardless of whether they live in South Korea or overseas.

2. SectorB Activity Features

SectorB targets countries from various regions around the world, and a total of four hacking groups activity were found to be active.

Targets were found in the Oceania region including Australia, the European region including the United Kingdom, and the East Asian region including South Korea.

Among this detected activity, some malware that had been used in the past was modified, or malware produced based on open source code was used for hacking activities.

Like before, hacking activity targeted at South Korea utilized Spear Phishing, which included Microsoft Word files containing Macros, and our analysis of the malware used shows that this campaign started in early 2018. In addition, SectorB targets started to include South Korean financial companies.

3. SectorC Activity Features

A total of three hacking groups activity were found to be active within SectorC.

Among this detected activity, SectorC01 activity was relatively more intense than others and SectorC activity was found to be aimed at South Europe including Spain, East Asia including Japan, and Eastern Europe including Ukraine and Poland.

Although hacking activities by SectorC groups around the world were conducted mainly to obtain information related to government agencies, they seem to be targeting Eastern Europe for other purposes based on the characteristics of their malware. SectorC still uses Spear Phishing with code execution vulnerabilities in Microsoft Word files or Microsoft Word files with macros for the initial infection in order to drop variants of their usual malware, although this time they have also included variants written in a different programming language. In addition, SectorC sometimes used only script and normal utility files for attacks on Eastern Europe.

4. SectorD Activity Features

A total of four hacking groups were found to be active within SectorD, and targets were concentrated in Middle Eastern countries, including Lebanon, Oman, Jordan, Saudi Arabia, Turkey, Iraq and Israel.

In addition to the use of Phishing websites, there were also cases where Spear Phishing was used with malware in the form of Microsoft Word files containing macros.

Although SectorD groups mainly utilize script-based malware, there were cases of hacking activities targeted at energy companies in Italy with ties to the Middle East which had reused the Wiper malware which was used in the past to disrupt normal system operations.

5. SectorE Activity Features

A total of three hacking groups activity were found to be active within SectorE, and targets were along the Central Asia region, which includes Pakistan, a political rival of SectorE, as well as Chinese companies.

The hacking activities of the SectorE took advantage of vulnerabilities in Microsoft Office, or Spear Phishing involving file-based malware that exploited vulnerabilities in InPage software, along with malware in the form of Word or Excel files containing macros.

In addition, the execution of malware is structured so that the download function is executed in the first step, and the next steps only work if the first one succeeded, reducing exposure to the outside as much as possible. However, as their malware, C2 IPs and C2 Domains were found to have some overlapping characteristics, it can be seen that SectorE groups share various hacking and malware production techniques.

6. SectorF Activity Features

SectorF activities were discovered targeting East Asia, including China and Japan.

They primarily utilizing Spear Phishing, attaching Microsoft Word files containing macros to emails.

While some of the code used in their malware was found to have been produced based on open source code used for penetration testing, others were found to be variants of their custom malware.

The full report detailing each event together with IOCs and recommendations is available to existing NSHC Threat Recon customers.

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These days, our lives are all connected to the internet and we all use it for many purposes. Most of us use this for positive purposes, but some have malicious intent.

The Threat Recon Team is the Cyber Threat Intelligence division of NSHC RedAlert Labs, and we track and define the Tactics, Techniques and Procedures of Threat Actor Groups who perform such malicious activity. This research allows us to understand how organizations can protect themselves against such groups.

Starting this year, our team’s researchers will publish our analysis here to share knowledge with other individuals and information security research teams to make a better and safer digital world.

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