OilRig’s persistent assaults utilizing cloud service-powered downloaders

ESET researchers analyzed a rising sequence of OilRig downloaders that the group has utilized in a number of campaigns all through 2022, to keep up entry to focus on organizations of particular curiosity – all positioned in Israel. These light-weight downloaders, which we named SampleCheck5000 (SC5k v1-v3), OilCheck, ODAgent, and OilBooster, are notable for utilizing certainly one of a number of official cloud service APIs for C&C communication and knowledge exfiltration: the Microsoft Graph OneDrive or Outlook APIs, and the Microsoft Workplace Alternate Net Companies (EWS) API.

In all circumstances, the downloaders use a shared (e-mail or cloud storage) OilRig-operated account to change messages with the OilRig operators; the identical account is often shared by a number of victims. The downloaders entry this account to obtain instructions and extra payloads staged by the operators, and to add command output and staged information.

We found the earliest of the sequence, SC5k (v1) downloader, in November 2021, when it was utilized in OilRig’s Outer House marketing campaign, documented in our latest blogpost. Within the present blogpost, we deal with the entire SC5k successors that OilRig developed all through 2022, with a brand new variation launched each few months; we may even take a better have a look at the mechanisms employed by these downloaders. We additionally evaluate these downloaders to different OilRig backdoors that use email-based C&C protocols, and that had been reported earlier this 12 months by Pattern Micro (MrPerfectionManager) and Symantec (PowerExchange).

Lastly, this blogpost additionally expands on our LABScon 2023 presentation, the place we drilled down into how OilRig retains entry to chose Israeli organizations: the entire downloaders studied on this blogpost had been deployed in networks that had been beforehand affected by a number of OilRig instruments, which underlines the truth that OilRig is persistent in focusing on the identical organizations, and decided to maintain its foothold in compromised networks.

Key factors of this blogpost:

• OilRig actively developed and used a sequence of downloaders with an identical logic all through 2022: three new downloaders – ODAgent, OilCheck, OilBooster – and newer variations of the SC5k downloader.
• The downloaders use numerous official cloud service APIs for C&C communication and knowledge exfiltration: Microsoft Graph OneDrive API, Microsoft Graph Outlook API, and Microsoft Workplace EWS API.
• Targets, all in Israel, included a company within the healthcare sector, a producing firm, an area governmental group, and different organizations.
• All targets had been beforehand affected by a number of OilRig campaigns.

Attribution

OilRig, often known as APT34, Lyceum, Crambus, or Siamesekitten, is a cyberespionage group that has been energetic since at the least 2014 and is generally believed to be primarily based in Iran. The group targets Center Jap governments and a wide range of enterprise verticals, together with chemical, vitality, monetary, and telecommunications.

OilRig carried out the DNSpionage marketing campaign in 2018 and 2019, which focused victims in Lebanon and the United Arab Emirates. In 2019 and 2020, OilRig continued its assaults with the HardPass marketing campaign, which used LinkedIn to focus on Center Jap victims within the vitality and authorities sectors. In 2021, OilRig up to date its DanBot backdoor and commenced deploying the Shark, Milan, and Marlin backdoors, as talked about within the T3 2021 situation of the ESET Menace Report. In 2022 and 2023, the group carried out a number of assaults towards native authorities entities and healthcare organizations in Israel, utilizing its new backdoors Photo voltaic and Mango. In 2023, OilRig focused organizations within the Center East with the PowerExchange and MrPerfectionManager backdoors, and associated instruments to reap inner mailbox account credentials after which to leverage these accounts for exfiltration.

We attribute SC5k (v1-v3), ODAgent, OilCheck, and OilBooster downloaders to OilRig with a excessive stage of confidence, primarily based on these indicators:

• Targets:
  • These downloaders had been deployed solely towards Israeli organizations, which aligns with typical OilRig focusing on.
  • The noticed verticals of the victims additionally align with OilRig’s pursuits – for instance, we now have seen OilRig beforehand focusing on the Israeli healthcare sector, in addition to the native authorities sector in Israel.
• Code similarities:
  • The SC5k v2 and v3 downloaders developed naturally from the preliminary model, which was beforehand utilized in an OilRig Outer House marketing campaign. ODAgent, OilCheck and OilBooster share related logic, and all use numerous cloud service suppliers for his or her C&C communications, as do SC5k, Marlin, PowerExchange, and MrPerfectionManager.
  • Whereas not distinctive to OilRig, these downloaders have a low stage of sophistication and are sometimes unnecessarily noisy on the system, which is a apply we beforehand noticed in its Out to Sea marketing campaign.

Overview

In February 2022, we detected a brand new OilRig downloader, which we named ODAgent primarily based on its filename: ODAgent.exe. ODAgent is a C#/.NET downloader that, just like OilRig’s Marlin backdoor, makes use of the Microsoft OneDrive API for C&C communications. Not like Marlin, which helps a complete record of backdoor instructions, ODAgent’s slender capabilities are restricted to downloading and executing payloads, and to exfiltrating staged information.

ODAgent was detected within the community of a producing firm in Israel – curiously, the identical group was beforehand affected by OilRig’s SC5k downloader, and later by one other new downloader, OilCheck, between April and June 2022. SC5k and OilCheck have related capabilities to ODAgent, however use cloud-based e-mail companies for his or her C&C communications.

All through 2022, we noticed the identical sample being repeated on a number of events, with new downloaders being deployed within the networks of earlier OilRig targets: for instance, between June and August 2022, we detected the OilBooster, SC5k v1, and SC5k v2 downloaders and the Shark backdoor, all within the community of an area governmental group in Israel. Later we detected yet one more SC5k model (v3), within the community of an Israeli healthcare group, additionally a earlier OilRig sufferer.

SC5k is a C#/.NET software whose objective is to obtain and execute further OilRig instruments utilizing the Workplace Alternate Net Companies (EWS) API. The brand new variations launched modifications to make retrieval and evaluation of the malicious payloads more durable for analysts (SC5k v2), and new exfiltration performance (SC5k v3).

All of the downloaders, summarized in Determine 1, share an identical logic however have totally different implementations and present rising complexity over time, alternating C#/.NET binaries with C/C++ functions, various the cloud service suppliers misused for the C&C communication, and different specifics.

OilRig has solely used these downloaders towards a restricted variety of targets, all positioned in Israel and, in keeping with ESET telemetry, all of them had been persistently focused months earlier by different OilRig instruments. As it is not uncommon for organizations to entry Workplace 365 assets, OilRig’s cloud service-powered downloaders can thus mix extra simply into the common stream of community visitors – apparently additionally the rationale why the attackers selected to deploy these downloaders to a small group of particularly fascinating, repeatedly victimized targets.

As of this writing, the next (solely Israeli, as famous above) organizations had been affected:

• a producing firm (SC5k v1, ODAgent, and OilCheck),
• an area governmental group (SC5k v1, OilBooster, and SC5k v2),
• a healthcare group (SC5k v3), and
• different unidentified organizations in Israel (SC5k v1).

Sadly, we don’t have details about the preliminary assault vector used to compromise the targets mentioned on this blogpost – we will’t affirm whether or not the attackers have been in a position to efficiently compromise the identical organizations repeatedly, or in the event that they one way or the other managed to maintain their foothold within the community in between deploying numerous instruments.

Technical evaluation

Desk 1. A abstract of major traits of OilRig’s downloaders abusing official cloud service suppliers

SC5k downloader

The SampleCheck5000 (or SC5k) downloader is a C#/.NET software, and the primary in a sequence of OilRig’s light-weight downloaders that use official cloud companies for his or her C&C communication. We briefly documented the primary variant in our latest blogpost, and have since found two newer variants.

All SC5k variants use the Microsoft Workplace EWS API to work together with a shared Alternate mail account, as a technique to obtain further payloads and instructions, and to add knowledge. Electronic mail drafts and their attachments are the first automobile for the C&C visitors in all of the variations of this downloader, however the later variations improve the complexity of this C&C protocol (SC5k v3) and add detection evasion capabilities (SC5k v2). This part focuses on highlighting these variations.

Alternate account used for C&C communication

At runtime, SC5k connects to a distant Alternate server by way of the EWS API to acquire further payloads and instructions to execute from an e-mail account shared with the attacker (and often different victims). By default, a Microsoft Workplace 365 Outlook account is accessed by way of the https://outlook.office365.com/EWS/Alternate.asmx URL utilizing hardcoded credentials, however some SC5k variations even have the potential to hook up with different distant Alternate servers when a configuration file is current with a hardcoded identify (setting.key, set.idl) and the corresponding credentials inside.

Now we have seen the next e-mail addresses utilized by SC5k variations for C&C communication, the primary of which gave the downloader its identify:

• samplecheck5000@outlook.com
• FrancesLPierce@outlook.com
• SandraRCharles@outlook.com

In SC5k v2, the default Microsoft Alternate URL, e-mail handle, and password are usually not included in the principle module – as an alternative, the downloader’s code has been break up into a number of modules. Now we have detected solely variations of the principle software, which logs right into a distant Alternate server, iterates via emails within the Drafts listing, and extracts further payloads from their attachments. Nonetheless, this software relies on two exterior courses that weren’t current within the detected samples and are in all probability carried out within the lacking module(s):

• The category init ought to present an interface to acquire the e-mail handle, username, and password required to log into the distant Alternate account, and different configuration values from the opposite module.
• The category construction ought to implement features used for encryption, compression, executing downloaded payloads, and different helper features.

These modifications had been probably launched to make retrieval and evaluation of the malicious payloads more durable for analysts, as the 2 lacking courses are essential for figuring out the Alternate account used for malware distribution.

C&C and exfiltration protocol

In all variations, the SC5k downloader repeatedly logs right into a distant Alternate server utilizing the ExchangeService .NET class within the Microsoft.Alternate.WebServices.Knowledge namespace to work together with the EWS API. As soon as related, SC5k reads e-mail messages with attachments within the Drafts listing to extract attacker instructions and extra payloads. Conversely, in every connection, SC5k exfiltrates information from an area staging listing by creating new e-mail drafts in the identical e-mail account. The trail to the staging listing varies throughout samples.

Of curiosity is the best way each the operators and numerous cases of this downloader can distinguish between the various kinds of drafts within the shared e-mail account. For one, every e-mail draft has a <victimID> integrated, which permits the identical Alternate account for use for a number of OilRig victims:

• For v1 and v2, the downloader transmits the <victimID> as a customized attribute of the e-mail draft by way of the SetExtendedProperty methodology.
• For v3, the downloader incorporates the <victimID> into the From area of the e-mail draft.

The <victimID> is often generated utilizing the compromised system’s data, such because the system quantity ID or the pc identify, as proven in Determine 2.

Moreover, numerous e-mail properties can be utilized to differentiate between messages created by the operators (instructions, further payloads) and messages created by the malware cases (command outputs, exfiltrated information). SC5k v1 and v2 use file extensions (of the draft attachments) to make that distinction, whereas SC5k v3 makes use of the From and MailItem.Classes fields of the e-mail draft to differentiate between numerous actions. At every level, the e-mail drafts within the shared e-mail account can serve numerous functions, as summarized in Desk 2 and defined under. Observe that the e-mail addresses used within the From area are usually not real; as a result of SC5k by no means sends out any precise e-mail messages, these attributes are solely used to differentiate between totally different malicious actions.

Desk 2. Forms of e-mail messages utilized by SC5k v3 for C&C communications

Extra particularly, SC5k v3 processes (after which deletes) these e-mail messages from the shared Alternate account which have the From area set to <victimID>@outlook.com, and distinguishes between instructions and extra payloads by the message class (MailItem.Classes):

• For payloads, the connected file is XOR decrypted utilizing the hardcoded key &5z, then gzip decompressed and dumped within the working listing.
• For shell instructions, the draft attachment is base64 decoded, XOR decrypted, after which executed regionally utilizing cmd.exe or, within the case of SC5k v3, utilizing a customized command interpreter positioned beneath the identify <baseDirectory>*Ext.dll. This file is then loaded by way of Meeting.LoadFrom, and its lengthen methodology invoked with the command handed as an argument.

To speak with the attackers, SC5k v3 creates draft messages with a special From area: <victimID>@aol.com. Hooked up to those messages are outputs of beforehand acquired instructions, or contents of the native staging listing. Recordsdata are at all times gzip compressed and XOR encrypted earlier than being uploaded to the shared mailbox, whereas shell instructions and command outputs are XOR encrypted and base64 encoded.

Lastly, SC5k v3 repeatedly creates a brand new draft on the shared Alternate account with the From area set to <victimID>@yahoo.com, to point to the attackers that this downloader occasion remains to be energetic. This keep-alive message, whose development is proven in Determine 3, has no attachment and is renewed with every connection to the distant Alternate server.

Different OilRig instruments utilizing email-based C&C protocol

OilCheck, a C#/.NET downloader found in April 2022, additionally makes use of draft messages created in a shared e-mail account for each instructions of the C&C communication. Not like SC5k, OilCheck makes use of the REST-based Microsoft Graph API to entry a shared Microsoft Workplace 365 Outlook e-mail account, not the SOAP-based Microsoft Workplace EWS API. Whereas SC5k makes use of the built-in ExchangeService .NET class to create the API requests transparently, OilCheck builds the API requests manually. The primary traits of OilCheck are summarized in Desk 1 above.

Earlier in 2023, two different OilRig backdoors had been publicly documented: MrPerfectionManager (Pattern Micro, February 2023) and PowerExchange (Symantec, October 2023), each utilizing email-based C&C protocols to exfiltrate knowledge. A notable distinction between these instruments and OilRig’s downloaders studied on this blogpost is that the previous use the victimized group’s Alternate server to transmit e-mail messages from and to the attacker’s e-mail account. In distinction: with SC5k and OilCheck, each the malware and the operator accessed the identical Alternate account and communicated by creating e-mail drafts, by no means sending an precise message.

In any case, the brand new findings affirm the development of OilRig shifting away from the beforehand used HTTP/DNS-based protocols to utilizing official cloud service suppliers as a technique to cover its malicious communication and to masks the group’s community infrastructure, whereas nonetheless experimenting with numerous flavors of such various protocols.

OilBooster downloader

OilBooster is a 64-bit transportable executable (PE) written in Microsoft Visible C/C++ with statically linked OpenSSL and Increase libraries (therefore the identify). Like OilCheck, it makes use of the Microsoft Graph API to hook up with a Microsoft Workplace 365 account. Not like OilCheck, it makes use of this API to work together with a OneDrive (not Outlook) account managed by the attackers for C&C communication and exfiltration. OilBooster can obtain information from the distant server, execute information and shell instructions, and exfiltrate the outcomes.

Overview

Upon execution, OilBooster hides its console window (by way of the ShowWindow API) and verifies that it was executed with a command line argument; in any other case it terminates instantly.

OilBooster then builds a <victimID> by combining the compromised pc’s hostname and username: <hostname>-<username>. This identifier is later used within the C&C communication: OilBooster creates a selected subdirectory on the shared OneDrive account for every sufferer, which is then used to retailer backdoor instructions and extra payloads (uploaded by the operators), command outcomes, and exfiltrated knowledge (uploaded by the malware). This fashion, the identical OneDrive account could be shared by a number of victims.

Determine 4 exhibits the construction of the shared OneDrive account and the native working listing, and summarizes the C&C protocol.

As proven in Determine 4, the OilRig operator uploads backdoor instructions and extra payloads to the victim-specific listing on OneDrive, as information with the .doc and .docx extensions, respectively. On the opposite finish of the C&C protocol, OilBooster uploads command outcomes and exfiltrated knowledge as information with the .xls and .xlsx extensions, respectively. Observe that these are usually not real Microsoft Workplace information, however reasonably JSON information with XOR-encrypted and base64-encoded values.

Determine 5 exhibits OilBooster spawning cases of two threads in an indefinite loop, sleeping for 153,123 milliseconds after every iteration:

Each threads work together with the shared OneDrive account:

1. A downloader thread handles C&C communication and executes downloaded payloads.
2. An exfiltration thread exfiltrates knowledge from the native staging listing.

The downloader thread connects to the attacker-controlled OneDrive account and iterates via all information with the .doc and .docx extensions, that are then downloaded, decrypted, and parsed with a purpose to extract and execute further payloads on the compromised host. An area subdirectory named gadgets within the present working listing (the place OilBooster is deployed) is used to retailer the downloaded information. As proven in Determine 6, every connection try is dealt with in a separate thread occasion, launched as soon as each 53,123 milliseconds.

The exfiltration thread iterates over one other native subdirectory, named tempFiles, and exfiltrates its contents to the shared OneDrive account, that are uploaded there as particular person information with the .xlsx extension. The staging listing is cleared this manner as soon as each 43,123 milliseconds in a separate thread occasion, as additionally seen in Determine 6.

Community communication

For C&C communication and exfiltration, OilBooster makes use of the Microsoft Graph API to entry the shared OneDrive account, utilizing a wide range of HTTP GET, POST, PUT, and DELETE requests to the graph.microsoft.com host over the usual 443 port. For brevity, we may even refer to those requests as OneDrive API requests. The encrypted communication is facilitated by the statically linked OpenSSL library, which handles the SSL communication.

To authenticate with the OneDrive account, OilBooster first obtains the OAuth2 entry token from the Microsoft id platform (the authorization server) by sending a POST request with the next physique over port 443 to login.microsoftonline.com/widespread/oauth2/v2.0/token, utilizing hardcoded credentials:

client_id=860b23a7-d484-481d-9fea-d3e6e129e249
&redirect_uri=https://login.reside.com/oauth20_desktop.srf
&client_secret=<redacted>
&refresh_token=<redacted>
&grant_type=refresh_token

OilBooster obtains a brand new entry token this manner, which will likely be used within the Authorization header of the next OneDrive API requests, together with a brand new refresh token. OilBooster additionally has a backup channel to request a brand new refresh token from its C&C server after 10 consecutive unsuccessful connections to the OneDrive server. As proven in Determine 7, the brand new token could be acquired by sending a easy HTTP GET request on port 80 to host1[.]com/rt.ovf (a official, probably compromised web site), which must be adopted by the brand new refresh token in cleartext within the HTTP response.

The assorted community connections made by OilBooster are summarized in Determine 8.

Downloader loop

Within the downloader loop, OilBooster repeatedly connects to the shared OneDrive account to get hold of a listing of information with the .docx and .doc extensions within the victim-specific subdirectory named <victimID>/gadgets/ by sending an HTTP GET request over port 443 to this URL:

graph.microsoft.com/v1.0/me/drive/root:/<victimID>/gadgets:/kids?$filter=endsWith(identify,’.doc’)%20orpercent20endsWith(identify,’.docx’)&$choose=id,identify,file

If the connection just isn’t profitable (the HTTP_STATUS_DENIED response standing) after 10 makes an attempt, OilBooster connects to its fallback C&C server, host1[.]com/rt.ovf, to accumulate a brand new refresh token, as mentioned earlier.

Alternatively, if the desired listing doesn’t but exist (HTTP_STATUS_NOT_FOUND), OilBooster first registers the sufferer on the shared OneDrive account by sending an HTTP POST request over port 443 to this URL: graph.microsoft.com/v1.0/me/drive/gadgets/root:/<victimID>:/kids with the JSON string {“identify”: “gadgets”,”folder”:{}} because the request physique, as proven in Determine 9. This request creates the entire listing construction <victimID>/gadgets on the identical time, which can later be utilized by the attackers to retailer instructions and extra payloads disguised as .doc and .docx information.

On subsequent connections (with HTTP_STATUS_OK), OilBooster processes these information to extract and execute payloads. OilBooster first downloads every file from the OneDrive account and deletes it from OneDrive after processing the file.

Processing .docx information

Observe the pointless creation of a number of information within the course of – that is typical for OilRig. We beforehand described the group’s noisy operations on compromised hosts in its Out to Sea marketing campaign.

Exfiltration loop

Within the exfiltration thread, OilBooster loops over the contents of the native listing named <currentdir>tempFiles, and uploads the file contents to the sufferer’s folder on the shared OneDrive account. Every file is processed on this manner:

• OilBooster gzip compresses the unique file <filename>.<authentic extension> and writes the end result to a file named <filename>.<authentic extension>.xlsx in the identical listing.
• It then encrypts the compressed file utilizing an XOR cipher and .<authentic extension> as the important thing. If there isn’t any file extension, 4cx is used because the default key.

Lastly, the encrypted file is uploaded to the OneDrive account, and the native file is deleted.

ODAgent downloader: OilBooster’s precursor

ODAgent is a C#/.NET software that makes use of the Microsoft Graph API to entry an attacker-controlled OneDrive account for C&C communication and exfiltration – briefly, ODAgent is loosely a C#/.NET precursor of OilBooster. Just like OilBooster, ODAgent repeatedly connects to the shared OneDrive account and lists the contents of the victim-specific folder to acquire further payloads and backdoor instructions.

As proven in Determine 10, ODAgent then parses the metadata for every distant file. Subsequently, it makes use of the worth of the mimeType key related to the file to differentiate between backdoor instructions (formatted as JSON information) and encrypted payloads – that is not like OilBooster, which makes use of file extensions for that distinction. After processing a file regionally, ODAgent deletes the unique from the distant OneDrive listing by way of the OneDrive API.

If the downloaded file is a JSON file, ODAgent parses the a1 (command ID), a2 (encrypted backdoor command) and a3 (secret) arguments. It first derives the session key by XORing the offered secret with the hardcoded worth 15a49w@]. Then, it base64 decodes and XOR decrypts the backdoor command utilizing this session key. Desk 3 lists all backdoor instructions supported by ODAgent.

Desk 3. Backdoor instructions supported by ODAgent

Backdoor command	Description
odt>	Returns the trail to the present working listing.
dly><delaytime>	Configures the variety of seconds to attend after every connection to <delaytime>.
<commandline>	Executes the desired <commandline> by way of the native API and returns the command output.

Different (non-JSON) information downloaded from the shared OneDrive account are information and extra payloads, each encrypted. ODAgent XOR decrypts these information with the hardcoded key 15a49w@], and drops them within the native <currentdir>o listing beneath the identical filename. If the unique file has a .c extension, its content material can be gzip decompressed (and the extension is then dropped from the filename).

On the finish of every connection, ODAgent uploads the contents of the native listing <currentdir>i to the <victimID>/i listing on the shared OneDrive account, preserving the unique filenames with the added .c extension.

Conclusion

For any inquiries about our analysis revealed on WeLiveSecurity, please contact us at threatintel@eset.com.
ESET Analysis presents non-public APT intelligence stories and knowledge feeds. For any inquiries about this service, go to the ESET Menace Intelligence web page.

IoCs

Recordsdata

Community

MITRE ATT&CK methods

This desk was constructed utilizing model 14 of the MITRE ATT&CK framework.