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For years, the Center East has maintained its fame as a fertile floor for superior persistent threats (APTs). Within the midst of routine monitoring of suspicious actions on the techniques of high-profile prospects, some primarily based on this area, ESET Analysis stumbled upon a really refined and unknown backdoor that now we have named Deadglyph. We derived the title from artifacts discovered within the backdoor (resembling 0xDEADB001, proven additionally in Desk 1), coupled with the presence of a homoglyph assault. To the very best of our information, that is the primary public evaluation of this beforehand undocumented backdoor, utilized by a gaggle that reveals a notable diploma of sophistication and experience. Primarily based on the concentrating on and extra proof, we attribute Deadglyph with excessive confidence to the Stealth Falcon APT group.

Deadglyph’s structure is uncommon because it consists of cooperating parts – one a local x64 binary, the opposite a .NET meeting. This mix is uncommon as a result of malware sometimes makes use of just one programming language for its parts. This distinction may point out separate growth of these two parts whereas additionally making the most of distinctive options of the distinct programming languages they make the most of. Completely different language may also be harnessed to hinder evaluation, as a result of blended code is tougher to navigate and debug.

The normal backdoor instructions are usually not carried out within the backdoor binary; as an alternative, they’re dynamically acquired by it from the command and management (C&C) server within the type of further modules. This backdoor additionally options a variety of capabilities to keep away from being detected.

On this blogpost, we take a better take a look at Deadglyph and supply a technical evaluation of this backdoor, its objective, and among the further parts we obtained. We’re additionally presenting our findings about Deadglyph on the LABScon 2023 convention.

Key factors of the blogpost:

• ESET Analysis found a classy backdoor with uncommon structure that now we have named Deadglyph.
• The primary parts are encrypted utilizing a machine-specific key.
• Conventional backdoor instructions are carried out by way of further modules acquired from its C&C server.
• We obtained three out of many modules – course of creator, file reader, and information collector.
• We attribute Deadglyph to the Stealth Falcon group.
• Moreover, we discovered a associated shellcode downloader; we postulate it may probably be used for set up of Deadglyph.

The sufferer of the analyzed infiltration is a governmental entity within the Center East that was compromised for espionage functions. A associated pattern discovered on VirusTotal was additionally uploaded to the file-scanning platform from this area, particularly from Qatar. The focused area is depicted on the map in Determine 1.

Stealth Falcon (often known as Challenge Raven or FruityArmor) is a menace group linked to the United Arab Emirates in line with MITRE. Energetic since 2012, Stealth Falcon is thought to focus on political activists, journalists, and dissidents within the Center East. It was first found and described by Citizen Lab, which printed an evaluation of a marketing campaign of adware assaults in 2016.

In January 2019, Reuters printed an investigative report on Challenge Raven, an initiative allegedly using former NSA operatives and aiming on the identical varieties of targets as Stealth Falcon. Primarily based on these two reviews referring to the identical targets and assaults, Amnesty Worldwide has concluded (proven in Determine 2) that Stealth Falcon and Challenge Raven truly are the identical group.

In September 2019, we printed analysis on a backdoor, attributed to Stealth Falcon, that used an uncommon approach, Background Clever Switch Service, for C&C communication. We now reveal the results of our in-depth evaluation of what presumably is the most recent addition to Stealth Falcon’s espionage toolset.

Deadglyph backdoor

Deadglyph’s loading chain consists of a number of parts, as illustrated in Determine 3. The preliminary element is a registry shellcode loader, which hundreds shellcode from the registry. This extracted shellcode, in flip, hundreds the native x64 a part of the backdoor – the Executor. The Executor subsequently hundreds the .NET a part of the backdoor – the Orchestrator. Notably, the one element on system’s disk as a file is the preliminary element, which is within the type of a Dynamic Hyperlink Library (DLL). The remaining parts are encrypted and saved inside a binary registry worth.

Whereas the exact methodology of the preliminary compromise vector shouldn’t be but decided, our suspicion is that an installer element is concerned in deploying additional parts and establishing persistence throughout the system.

In the remainder of this part, we analyze every element.

Registry shellcode loader

Deadglyph’s preliminary element is a tiny DLL with a single export, named 1. This element is persevered utilizing Home windows Administration Instrumentation (WMI) occasion subscription and serves as a registry shellcode loader. It’s executed by way of the command line rundll32 C:WINDOWSSystem32pbrtl.dll,#1.

The registry shellcode loader begins its operation by decrypting the trail to the encrypted shellcode saved throughout the Home windows registry, utilizing RC4. We suspect the trail is exclusive for every sufferer; within the case analyzed right here, the registry path was:

SoftwareClassesCLSID{5abc7f42-1112-5099-b082-ce8d65ba0c47}cAbRGHLg

The basis registry key’s both HKLM or HKCU, relying on whether or not the present course of is operating with elevated privileges or not. The identical logic will be present in additional parts.

Following this, the loader derives a machine-specific RC4 key utilizing the system UUID retrieved from the uncooked SMBIOS firmware desk. Utilizing this key, it hundreds, decrypts, after which executes the shellcode. You will need to spotlight that this key derivation strategy ensures that correct decryption gained’t happen if the loader is executed on a special pc.

Apparently, the loader may also be configured by a flag in its .knowledge part to make use of a hardcoded key to decrypt the shellcode, as an alternative of the machine-specific one.

We noticed a homoglyph assault mimicking Microsoft Company within the VERSIONINFO useful resource of this and different PE parts. This methodology employs distinct Unicode characters that seem visually comparable, however on this case not an identical, to the unique characters, particularly Greek Capital Letter San (U+03FA, Ϻ) and Cyrillic Small Letter O (U+043E, о) in Ϻicrоsоft Corpоratiоn.

Registry shellcode

Comprised of two components, the registry shellcode consists of a decryption routine and an encrypted physique. First, the decryption routine rotates every byte of the encrypted physique to the left by one (ROL 0x01). Subsequently, management is transferred to this decrypted physique. The decrypted physique consists of a PE loader and a PE file, the latter being the Executor, which represents the native a part of the backdoor. This loader is chargeable for parsing and loading the related PE file.

Executor

The Executor is the native x64 a part of the Deadglyph backdoor, which does the next:

• hundreds its configuration,
• initializes the .NET runtime,
• hundreds the embedded .NET a part of the backdoor (the Orchestrator), and
• acts as a library for the Orchestrator.

First, two default configurations embedded within the .knowledge part are AES-decrypted. The configurations embody varied parameters, together with encryption keys, security and evasion settings, and the entry level of the following element.

In the course of the preliminary execution, these two default configurations are saved throughout the Home windows registry, from the place they’re loaded on subsequent runs, enabling the implementation of updates. The registry path for every configuration is generated with the next format:

HKLMSoftwareClassesCLSID{<variable_GUID>}(Default)

<variable_GUID> is a generated GUID, which is exclusive to every sufferer.

Following this, the .NET runtime is initialized, then the Executor RC4-decrypts the .NET a part of the backdoor often called the Orchestrator. The Orchestrator is situated throughout the .rsrc part of the Executor. The configuration specifies the Orchestrator’s execution methodology as an entry level. Furthermore, a definite construction is offered to facilitate accessibility of the Executor’s features by the Orchestrator.

After launching the Orchestrator, the Executor acts as a help library for the Orchestrator. The Executor accommodates many fascinating features; we describe a few of them within the following part, in context of their utilization by the Orchestrator and additional loaded modules.

Orchestrator

Written in .NET, the Orchestrator is the principle element of the Deadglyph backdoor. This element’s major function includes establishing communication with the C&C server and executing instructions, usually facilitated by way of the middleman function of the Executor. In distinction to the previous parts, the Orchestrator is obfuscated, using .NET Reactor. Internally, the backdoor is known as agent, which is a standard title for the shopper half in varied post-exploitation frameworks.

Initialization

The Orchestrator first hundreds its configuration and two embedded modules, every accompanied by its personal set of configurations, from sources. These sources are Deflate compressed and AES encrypted. They’re referenced by an ID that’s SHA-1 hashed right into a useful resource title. An outline of those sources is offered in Desk 1.

Desk 1. Orchestrator sources

The configuration of the Orchestrator and embedded modules is saved in XML format. An instance of an Orchestrator configuration is proven in Determine 4.

The outline of Orchestrator configuration entries is proven in Desk 2.

Desk 2. Orchestrator configuration entries

After the useful resource parts are loaded, a number of threads are created to hold out distinct duties. Considered one of these threads is chargeable for conducting surroundings checks, a perform carried out throughout the Executor. One other thread is dedicated to establishing periodic communication with the C&C server, enabling the retrieval of instructions. Lastly, a set of three threads is employed for the aim of executing acquired instructions and subsequently transmitting any generated output again to the C&C server.

The environment-checking thread displays operating processes to establish undesirable ones. This thread operates with two distinct lists of course of names. If a course of on the primary listing is detected, C&C communication and command execution is paused till the undesirable course of not exists. If there’s a match for any course of on the second listing, the backdoor instantly quits and uninstalls itself.

Neither listing was configured within the analyzed occasion, so we don’t know what processes may sometimes be checked for; we imagine it’s in all probability supposed to evade evaluation instruments that might detect suspicious exercise and result in discovery of the backdoor.

Communication

The Orchestrator makes use of two embedded modules for C&C communication – Timer and Community. Just like the Orchestrator, these modules are obfuscated with .NET Reactor. The configuration for each modules is provided by the Orchestrator. Inside the Orchestrator, a preset configuration for the modules is included; optionally, the Orchestrator also can load an up to date configuration model from the registry:

HKLMSoftwareClassesCLSID{<variable_GUID>}<mod_cfg_res_ID>

The backdoor accommodates an fascinating security measure associated to communication. If the backdoor is unable to ascertain communication with the C&C server for a period surpassing a predefined threshold, configured throughout the Executor, a self-uninstallation mechanism is triggered. This time threshold is laid out in hours and was set at one hour within the examined case.

This strategy serves a twofold objective. On one hand, it prevents the technology of redundant community requests in direction of an inaccessible server. Alternatively, it reduces the possibilities of subsequent detection if the operators lose management over the backdoor.

Timer module

This small module executes the desired callback at a configurable interval. It’s utilized by the Orchestrator together with the Community module to speak with the C&C server periodically. To forestall the creation of detectable patterns in community logs, the execution interval is topic to randomization, primarily based on a share specified within the configuration. Within the analyzed occasion, the interval was set to 5 minutes, with a ±20% variation launched for randomness.

One other methodology to keep away from detectable community patterns in periodic communication will be present in technology of requests despatched to the C&C server. This mechanism, carried out within the Executor, includes the inclusion of padding of various size, comprised of random bytes, throughout the requests, leading to requests of numerous sizes.

Community module

The Community module implements communication with the C&C servers laid out in its configuration. It may possibly ship knowledge to a C&C server utilizing HTTP(S) POST requests. Notably, it presents a number of mechanisms to amass proxy configuration particulars. This function suggests a possible deal with environments the place direct web entry shouldn’t be out there.

An instance of a decrypted (and beautified) configuration is proven in Determine 5.

Configuration entries comprise particulars associated to community communications – C&C URLs, HTTP Consumer-Agent, and optionally a proxy configuration.

When speaking with the C&C server, a customized binary protocol with encrypted content material is used beneath HTTPS.

Instructions

The Orchestrator receives instructions from the C&C server within the type of duties, that are queued for execution. There are three sorts of duties processed:

• Orchestrator duties,
• Executor duties, and
• Add duties.

The primary two sorts are acquired from the C&C server and the third is created internally to add the output of instructions and errors.

Orchestrator duties

Orchestrator duties provide the power to handle the configuration of the Community and Timer modules, and in addition to cancel pending duties. The overview of Orchestrator duties is proven in Desk 3.

Desk 3. Orchestrator duties

Executor duties

Executor duties provide the power to handle the backdoor and execute further modules. It’s notable that the standard backdoor performance shouldn’t be inherently current throughout the binary itself. As an alternative, these features are obtained from the C&C server within the type of PE information or shellcode. The complete extent of the backdoor’s potential stays unknown with out these further modules, which successfully unlock its true capabilities. An outline of module duties is proven in Desk 4, which incorporates particulars in regards to the few recognized modules. Equally, Desk 5 offers an summary of administration duties related to the Executor.

Desk 4. Executor duties – modules

Desk 5. Executor duties – administration

The command that units the Executor configuration can change the:

• undesirable course of lists,
• time threshold of C&C communication failure, and
• time restrict for execution of further modules.

Modules

We managed to acquire three distinctive modules from the C&C server, every akin to a special Executor activity sort, as proven in Desk 4. Primarily based on out there data, we estimate there are 9 to 14 modules in complete. Because the modules are in reality backdoor instructions, they’ve one fundamental operation to execute after which optionally return their output. The modules we obtained are DLLs with one unnamed export (ordinal 1), by which they resolve essential API features and name the principle perform.

When executed, the modules are supplied with an API decision perform, which might resolve Home windows APIs and customized Executor APIs. The Home windows APIs are referenced by a DWORD hash, calculated from the title of the API and its DLL. Small hash values (<41) are handled specifically, referencing the Executor API perform. The Executor API contains a complete of 39 features which are accessible to the modules. These features pertain to a wide range of operations, together with:

• file operations,
• encryption and hashing,
• compression,
• PE loading,
• entry Token Impersonation, and
• utility.

In the remainder of this part, we describe the modules that we obtained.

Course of creator

Module 0x69 executes the desired command line as a brand new course of and offers the ensuing output again to the Orchestrator. The method will be created beneath a special consumer, and its execution time will be restricted. Notably, an uncommon Job API is used on this module’s performance.

This module was served with the command line cmd.exe /c tasklist /v.

We assume it serves as an idle command issued mechanically, whereas the operators look forward to one thing fascinating to occur on the compromised pc.

Information collector

Module 0x6C collects in depth details about the pc by way of WMI queries and passes it again to the Orchestrator. Details about the next is collected:

• working system,
• community adapters,
• put in software program,
• drives,
• companies,
• drivers,
• processes,
• customers,
• surroundings variables, and
• safety software program.

File reader

Module 0x64 reads the desired file and passes the content material again to the Orchestrator. Optionally, it may possibly delete the file after studying.

We noticed this module used to retrieve the sufferer’s Outlook knowledge file

c:Customers<redacted>AppDataLocalMicrosoftOutlookoutlook.ost.

Chain with shellcode downloader

Within the strategy of investigating Deadglyph, we encountered a doubtful CPL file signed with an expired certificates and no countersignature with a timestamp, which had been uploaded to VirusTotal from Qatar. Upon nearer examination, it grew to become evident that this CPL file functioned as a multistage shellcode downloader, sharing sure code resemblances with Deadglyph. The loading chain is illustrated in Determine 6.

In its preliminary kind, which serves as the primary stage, this file anticipates having a .cpl extension (Management Panel file) and is supposed to be executed by way of a double-click motion. Upon execution on this method, the embedded shellcode undergoes XOR decryption, and the operating processes are checked to establish an acceptable host course of for subsequent injection.

If avp.exe (a Kaspersky endpoint safety course of) is operating, %windirpercentsystem32UserAccountBroker.exe is used. In any other case, the default browser is used. Then, it creates the host course of in a suspended state, injects the shellcode by hijacking its important thread, and resumes the thread.

The second stage, the shellcode, consists of two components. The primary a part of the shellcode resolves API hashes, utilizing the identical distinctive hash calculation approach employed in Deadglyph, and decrypts strings with course of names. It begins a self-delete thread tasked with overwriting and subsequently erasing the first-stage file. Following this, the shellcode proceeds to examine the presently lively processes, concentrating on a safety resolution.

If any of the desired processes are detected, the shellcode creates a sleeper thread with the bottom precedence (THREAD_PRIORITY_IDLE) and permits it to stay lively for a period of 60 seconds earlier than terminating its operation. This interval is probably going carried out as a precautionary measure to evade sure detection mechanisms employed by safety options. Lastly, the shellcode proceeds to invoke the execution of the second a part of its code.

The second a part of the shellcode hundreds an embedded PE file with stage three and calls its export with ordinal quantity 1.

The third stage, a DLL, serves as a .NET loader and accommodates the payload in its .rsrc part.

To load the payload, the .NET runtime is initialized. In the course of the .NET initialization, two intriguing strategies are carried out, seemingly supposed to evade Home windows Antimalware Scan Interface (AMSI) scanning:

• The .NET loader quickly hooks the GetModuleHandleW import within the loaded clr.dll, whereas calling ICorRuntimeHost::Begin. The hook tampers with the return worth when GetModuleHandleW is named with NULL. It returns a pointer to a dummy PE with no sections.
• It then subtly patches the AmsiInitialize import title string within the .rdata part of the loaded clr.dll to amsiinitialize.

The fourth stage is a .NET meeting, obfuscated with ConfuserEx, that serves as a shellcode downloader. First, it XOR-decrypts its configuration in XML format from its sources. A beautified model of the extracted configuration is introduced in Determine 7. The configuration entries comprise particulars associated to community communication and blocklisted processes.

Earlier than continuing, it checks the operating processes towards a listing of blocklisted processes from the configuration. If a match is detected, the execution halts. You will need to notice that within the analyzed occasion, this blocklist wasn’t arrange.

Subsequent, it sends an HTTP GET request to the C&C server to retrieve some shellcode, utilizing parameters specified within the configuration (URL, Consumer-Agent, and optionally Proxy). Regrettably, throughout our investigation we have been unable to amass any shellcode from the C&C server. Nonetheless, we hypothesize that the content material being retrieved may probably function the installer for Deadglyph.

Following this, the retrieved shellcode is executed inside a newly created thread. After ready till the shellcode thread finishes execution, the shellcode downloader removes all information situated within the listing %WINDIRpercentServiceProfilesLocalServiceAppDataLocalTempTfsStoreTfs_DAV.

Lastly, it makes an try to delete itself after a 20-second interval, using the following command, earlier than concluding its operation and exiting:

cmd.exe alternative /C Y /N /D Y /T 20 & Del /f /q <current_process_exe_path>

This self-deletion doesn’t make sense on this chain. This is because of the truth that the shellcode downloader is executed inside a browser or system course of after being injected, somewhat than working as an impartial executable. Furthermore, the preliminary file was already deleted by the second stage. This statement means that the shellcode downloader may not be an unique payload of this chain and might also be used individually in different operations.

Conclusion

We’ve found and analyzed a classy backdoor utilized by the Stealth Falcon group that now we have named Deadglyph. It has an uncommon structure, and its backdoor capabilities are offered by its C&C within the type of further modules. We managed to acquire three of those modules, uncovering a fraction of Deadglyph’s full capabilities.

Notably, Deadglyph boasts a variety of counter-detection mechanisms, together with steady monitoring of system processes and the implementation of randomized community patterns. Moreover, the backdoor is able to uninstalling itself to reduce the chance of its detection in sure circumstances.

Moreover, our investigation led us to the invention of a compelling multistage shellcode downloader chain on VirusTotal. We suspect this downloader chain is probably going leveraged within the set up strategy of Deadglyph.

For any inquiries about our analysis printed on WeLiveSecurity, please contact us at threatintel@eset.com.
ESET Analysis presents personal APT intelligence reviews and knowledge feeds. For any inquiries about this service, go to the ESET Risk Intelligence web page.

IoCs

Recordsdata

Certificates

C&C servers

MITRE ATT&CK strategies

This desk was constructed utilizing model 13 of the MITRE ATT&CK framework.