Storm-0324 gathers over Microsoft Teams

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An initial access broker associated with several different ransomware operations is now conducting Microsoft Teams phishing attacks

Alex Scroxton,
Security Editor

Published: 13 Sep 2023 12:08

A threat actor tracked in Microsoft’s taxonomy as Storm-0324 has been observed switching up its tactics to incorporate social engineering phishing attacks conducted via Microsoft Teams, Redmond has revealed.

Storm-0324, a so-called initial access broker (IAB), is linked to several prolific and dangerous ransomware operations, including some known to have deployed the Clop, Gandcrab, Maze and REvil lockers.

“Beginning in July 2023, Storm-0324 was observed distributing payloads using an open source tool to send phishing lures through Microsoft Teams chats,” wrote the Microsoft Threat Intelligence team.

“This activity is not related to the Midnight Blizzard social engineering campaigns over Teams that we observed beginning in May 2023. Because Storm-0324 hands off access to other threat actors, identifying and remediating Storm-0324 activity can prevent more dangerous follow-on attacks like ransomware.

From 2018 up until quite recently, the group’s activity has centred on distributing its malware, JSSLoader, on behalf of the ransomware-as-a-service (RaaS) actor Sangria Tempest – aka Elbrus, Carbon Spider, and FIN7 – using what Microsoft described as “highly evasive infection chains with payment and invoice lures” linking to a SharePoint site from whence the unwary download a malicious ZIP archive containing the payload.

But the threat actor now appears to be exploiting an issue in Teams that was first identified by Jumpsec researchers in June 2023, but left unpatched by Microsoft at the time, supposedly on the basis that it was not serious enough to fix right away.

This activity began in July – after the Jumpsec disclosure had received some attention – and likely involves the use of a publicly available tool called TeamsPhisher, a Python program that lets Teams tenant users attach files to messages sent to external tenants.

It is no stretch to see how this feature can be abused and this seems to be what Storm-0324 is doing, using it to send phishing lures leading to the malicious SharePoint site. Its lures are identified by the Teams platform as external ones, should external access be enabled, meaning they get through to potential victims quite easily.

Defenders have a number of options to harden their networks against these attacks, as set out by Microsoft.

“Microsoft takes these phishing campaigns very seriously and has rolled out several improvements to better defend against these threats,” the Threat Intel team wrote.

“In accordance with Microsoft policies, we have suspended identified accounts and tenants associated with inauthentic or fraudulent behaviour. We have also rolled out enhancements to the Accept/Block experience in one-on-one chats within Teams, to emphasise the externality of a user and their email address so Teams users can better exercise caution by not interacting with unknown or malicious senders.

“We rolled out new restrictions on the creation of domains within tenants and improved notifications to tenant admins when new domains are created within their tenant. In addition to these specific enhancements, our development teams will continue to introduce additional preventative and detective measures to further protect customers from phishing attacks.”

Why is this more dangerous than email phishing?

“This is a sophisticated phishing scam that will catch out many victims because they will not realise criminals can hijack on Microsoft Teams to carry out attacks,” said My1Login CEO Mike Newman.

Newman explained that while people tend to understand the techniques cyber criminals use to send phishing emails, Teams is more readily seen as an internal communications platform.

“Employees place more trust in the tool and are more likely to open and action documents they receive in chats,” he said.

“For organisations that are worried about this threat, it is essential to educate employees on all the different techniques criminals can use to launch phishing attacks – from emails, phone calls, SMS to messaging platforms.

“Furthermore, with many of these scams being developed to steal employee credentials, organisations can improve their defences by removing passwords from employee hands. This means even when highly sophisticated scams do reach user inboxes, they can’t be tricked into handing over their credentials because they simply do not know them,” he added.

Cofense senior cyber threat intelligence analyst Max Gannon added: “Chat systems such as Slack and Teams need to be acknowledged by organisations as something that poses the same threat level as credential phishing emails. Any system that can be manipulated to take advantage of a user’s trust can be used as a method of entry…. Treating any one source as being a non-issue or as having a negligible threat level can easily come back to haunt decision-makers.

“That said, training users in any one platform enables them to apply the same skills and skepticism to any other platform. These incidents really drive home the necessity of organisations using all the tools at their disposal to account for threats they haven’t even yet recognised.”