Ransomware Access Broker Steals Accounts via Microsoft Teams Phishing

Cyber Security Threat Summary:
Microsoft has reported a change in tactics by an initial access broker, previously associated with ransomware groups. This actor, identified as Storm-0324, has shifted its focus to Microsoft Teams phishing attacks as a means to infiltrate corporate networks. Storm-0324 is a financially motivated threat group with a history of deploying ransomware such as Sage and GandCrab in previous campaigns.

“FIN7 (aka Sangria Tempest and ELBRUS) was seen deploying Clop ransomware on victims' networks. It was also previously linked to Maze and REvil ransomware before the now-defunct BlackMatter and DarkSide ransomware-as-a-service (Raas) operations. "In July 2023, Storm-0324 began using phishing lures sent over Teams with malicious links leading to a malicious SharePoint-hosted file," Microsoft said on Tuesday. "For this activity, Storm-0324 most likely relies on a publicly available tool called TeamsPhisher."This open-source tool enables attackers to bypass restrictions for incoming files from external tenants and send phishing attachments to Teams users. It does this by exploiting a security issue in Microsoft Teams discovered by Jumpsec security researchers that Microsoft refused to address in July after saying that the flaw did "not meet the bar for immediate servicing. "Nevertheless, the issue was also exploited by APT29, the Russian Foreign Intelligence Service (SVR) hacking division, in attacks against dozens of organizations, including government agencies worldwide. While Microsoft did not provide details on the end goal of Storm-0324's attacks this time around, APT29's attacks aimed to steal the targets' credentials after tricking them into approving multifactor authentication (MFA) prompts" (BleepingComputer, 2023).

Security Officer Comments:
Microsoft has taken decisive action to combat Teams phishing attacks and safeguard its customers. The company has implemented significant improvements to enhance defenses against such threats. These improvements include identifying threat actors as "EXTERNAL" users when external access is enabled and enhancing the Accept/Block experience in one-on-one chats to raise awareness of external users. Microsoft has also imposed restrictions on domain creation within tenants and improved notifications for tenant administrators regarding new domain creations. In response to the Storm-0324 campaign, Microsoft suspended the tenants and accounts used in the attacks.

Suggested Correction(s):
Users should always be cautious of individuals or organizations that ask for personal information. Most companies will not ask for sensitive data from its customers. If in doubt, users should verify with the company itself to avoid any potential issues.

Users should always take a close look at the sender’s display name when checking the legitimacy of an email. Most companies use a single domain for their URLs and emails, so a message that originates from a different domain is a red flag.

As a general rule, users should not click links or download files even if they come from seemingly “trustworthy” sources.

Check for mismatched URLs. While an embedded URL might seem perfectly valid, hovering above it might show a different web address. In fact, users should avoid clicking links in emails unless they are certain that it is a legitimate link.

Users should always be on the lookout for any grammatical errors and spelling mistakes. Legitimate companies will often employ proofreaders and editors who ensure that the materials they send out are error-free.

Users should not be frightened or intimidated by messages that have an alarmist tone. They should double check with the company if they are uncertain about the status of their accounts.

Phishing emails are designed to be sent to a large number of people, so they need to be as impersonal as possible. Users should check whether the message contains a generic subject and greeting, as this can be a sign of a phishing attempt.

Although not every end user has access to advanced anti-phishing software, they can still use the built-in protection of their email clients to filter messages. One example is setting the email client to block all images unless approved.

Legitimate companies will never send confirmation emails unless there are specific reasons for doing so. In fact, most companies will avoid sending unsolicited messages unless it’s for company updates, newsletters, or advertising purposes.

Users should always take the context of an email or message into account. For example, most online accounts do away with viewable member numbers, so users should be wary if they receive emails containing a “member number” for services that generally don’t use them.

It is important to take note of unusual information in the text of the message. Any mentions of operating systems and software that are not typically used by consumers can often be indicators of a phishing attempt.

If it seems suspicious, it probably is. Users should always err on the side of caution when it comes to sending out personally identifiable information through messages and emails.