New OilRig Downloaders Abusing Microsoft Cloud APIs for C&C Communications

Threat actors engage in cyberespionage to gain the following advantages:-

• Strategic
• Political
• Economic
• Military

Hackers do so by stealing the following key things from the targeted organizations or nations:-

• Confidential data
• Intellectual property
• Classified information

Cybersecurity researchers at ESET recently identified that new OilRig downloaders are abusing Microsoft Cloud APIs for C&C communications.

Cyberespionage group OilRig, active since 2014, targets Middle Eastern governments and diverse industries. 

Notable campaigns include DNSpionage (2018-2019) and HardPass (2019-2020) using LinkedIn. Updates in 2021 include DanBot and new backdoors (Shark, Milan, Marlin). 

In 2022-2023, focused attacks on Israeli entities with Solar and Mango backdoors. In 2023, PowerExchange and MrPerfectionManager were used for mailbox credential harvesting and exfiltration in the Middle East.

OilRig Downloaders Abusing Microsoft Cloud

In Feb 2022, OilRig researchers found ODAgent, a new C#/.NET downloader using Microsoft OneDrive API. Unlike Marlin, ODAgent focuses on downloading, executing, and exfiltrating files. 

It hit an Israeli manufacturing company linked to prior OilRig attacks with SC5k and OilCheck. Throughout 2022, OilRig deployed new downloaders in familiar targets of an Israeli governmental network, like:-

• OilBooster
• SC5k v1
• SC5k v2
• Shark

Another SC5k (v3) surfaced in an Israeli healthcare organization, a previous victim. SC5k evolves, complicating payload retrieval (SC5k v2) and adding new exfiltration features (SC5k v3). Despite similarities, these downloaders differ in:-

• Implementation
• Complexity
• Tactics over time

OilRig targets limited Israel-based entities with downloaders that were previously attacked by other OilRig tools. The cloud-based downloaders seamlessly blend into normal network traffic, especially in Office 365 environments. 

SC5k, at runtime, connects to a remote Exchange server via EWS API, obtaining payloads and commands from a shared email account with the attacker. SC5k variations exist, accessing Exchange servers through hardcoded URLs and credentials. 

SC5k logs into the remote server that reads emails in the Drafts directory for payloads and exfiltrates files by creating new drafts. While the drafts have <victimID>, enabling one account for multiple victims. 

SC5k distinguishes between operator and malware-created drafts using file extensions (v1/v2) or email properties (v3). With fake “from addresses” to maintain stealth, the email drafts serve diverse purposes like:-

• Command execution
• Payload retrieval
• File exfiltration

In 2022 and 2023, OilRig unveiled tools like OilCheck and SC5k, exploiting legitimate cloud-based email service APIs for C&C communication. 

OilCheck, discovered in April 2022, diverges from SC5k by using Microsoft Graph API instead of EWS API. OilCheck crafts API requests manually. 

Two other OilRig backdoors opt for email-based C&C to exfiltrate data:-

• MrPerfectionManager (Feb 2023)
• PowerExchange (Oct 2023)

Unlike HTTP/DNS, OilRig adopts cloud services for stealth, shifting away from traditional protocols. SC5k and OilCheck employ shared Exchange accounts, using email drafts for communication, ensuring a covert approach. 

However, apart from this, OilRig continues to experiment with alternative protocols, hiding its malicious activities.

In 2022, OilRig unveiled new downloaders exclusively for Israeli targets, persistently hitting the same ones. 

All these lightweight yet potent tools opt for cloud service accounts, differing from internal infrastructure use seen in MrPerfectionManager and PowerExchange:-

• SC5k
• OilBooster
• ODAgent
• OilCheck

OilRig’s shift to cloud-based C&C channels signifies an ongoing strategy to hide their malicious activities and network infrastructure.