HomeWinBuzzer NewsStorm-0558 Attack on U.S. Gov: Other Microsoft Cloud Users Possibly at Risk

Storm-0558 Attack on U.S. Gov: Other Microsoft Cloud Users Possibly at Risk

The compromised key used in the attack was not just used to access individual accounts but might have granted access to entire organizations' Microsoft 365 systems.


In the wake of the recent disclosure by Security of a massive cyberattack by a Chinese group named Storm-0558, new details have emerged about the extent and sophistication of the attack. As previously reported, the group hacked into the email accounts of dozens of agencies and other organizations, exploiting a flaw in Microsoft's email security service. This breach, discovered by the firm Wiz, has raised serious concerns about the security of Microsoft's cloud services.

Breach used A Master Key to Microsoft 365 Accounts

Behind the Storm-0558 attack was a compromised Microsoft key, dubbed Storm-0558, which was used to authenticate countless accounts without the need for a password or any other form of user verification. This key is part of Microsoft's SAML (Security Assertion Markup Language) system, which is used to exchange authentication and authorization data between parties. In this case, the key was being used to generate SAML tokens that were then used to authenticate Microsoft 365 accounts. The discovery of the compromised key is a significant blow to Microsoft's security measures, as it shows that even the most secure systems can be compromised.

Scope: From Individual Accounts to Entire Organizations

The compromised key was not just used to access individual accounts. It was also used to gain access to entire organizations' Microsoft 365 systems. This means that the attackers could have potentially had access to a vast amount of sensitive data, including emails, documents, and other data stored in these systems. The discovery of the compromised key has raised serious questions about the security of Microsoft's SAML system. If a key can be compromised and used to authenticate accounts, then the entire system's security is in question. This is especially concerning given the widespread use of SAML for authentication in many other systems.

Microsoft's Response: Revoking the Key and Strengthening Security

In response to the discovery, Microsoft has revoked the compromised key and is working to strengthen its security measures. However, the damage has already been done, and it is unclear how many accounts were accessed using the compromised key. Microsoft has taken several steps to address the issue, including identifying the root cause, establishing durable tracking of the campaign, disrupting malicious activities, hardening the environment, notifying every impacted customer, and coordinating with multiple government entities. Microsoft has also blocked the campaign from Storm-0558 and continues to investigate and monitor the situation.

Mitigation Measures and Future Steps

According to a detailed analysis by Microsoft, the company has implemented several mitigations in response to the token forgery technique used by the actor. These include stopping the acceptance of tokens issued from GetAccessTokensForResource for renewal, blocking the usage of tokens signed with the acquired MSA key in OWA, and replacing the key to prevent the actor from using it to forge tokens. Microsoft has also shared indicators of compromise (IOCs) and recommended actions with the security community to help other organizations protect themselves from similar attacks.

A Wake-Up Call for Cybersecurity

While Microsoft has mitigated this activity on behalf of its customers, the incident underscores the persistent and evolving threats in the digital landscape. As threat actors continue to develop sophisticated techniques, organizations must remain vigilant and proactive in their cybersecurity efforts. Microsoft continues to monitor Storm-0558 activity and implement protections for its customers. For more information on how to protect your organization, visit Microsoft's Security Blog.

The Storm-0558 incident is a stark reminder of the importance of robust security measures. Even the most secure systems can be compromised, and organizations must be proactive in their security measures to protect their data and their customers. In the wake of this incident, Wiz has recommended that organizations review their security measures and ensure that they are up to date. This includes regularly updating passwords, using multi-factor authentication, and regularly monitoring for any suspicious activity. The Storm-0558 incident is a wake-up call for the cybersecurity world. It shows that even the most secure systems can be compromised and that constant vigilance is necessary to protect against these threats.

Markus Kasanmascheff
Markus Kasanmascheff
Markus is the founder of WinBuzzer and has been playing with Windows and technology for more than 25 years. He is holding a Master´s degree in International Economics and previously worked as Lead Windows Expert for Softonic.com.