The China-linked threat actors who stole the US State Department and other Microsoft customer emails may have acquired access to apps other than Exchange Online and Outlook.com.

According to Wiz Researchers, the compromised signing key was more potent than it first appeared to be and was not restricted to just those two services.

The threat actor may have been able to forge access tokens for a variety of Azure Active Directory applications, including any that supports personal account authentication, such as SharePoint, Teams, or OneDrive, as well as customer applications that support the “login with Microsoft” feature and multi-tenant applications under specific circumstances.

It is advised to organizations look for instances of forged token usage on any potentially compromised apps.

Overview of the Hack

Microsoft issued a warning earlier this month after an advanced persistent threat group it refers to as Storm-0558 breached the systems of around 25 customers globally, including several government clients.

The hackers purportedly obtained access to private emails from U.S. Commerce Secretary Gina Raimondo and other high-profile individuals.

The Cybersecurity and Infrastructure Security Agency (CISA) collaborated with Microsoft on efforts to mitigate the damage and further examine how the hackers initially got access after government authorities informed Microsoft about the incident.

According to a statement by Microsoft earlier this month, the threat actor created access tokens for Exchange Online and Outlook.com after gaining access to an MSA consumer signing key.

The Wiz study reveals that the key gives users access to a significantly larger range of applications.

The signing keys used by identity providers are among the most potent trade secrets today. They are far more potent than TLS keys, for instance.

To have a major impact, an attacker would still need to impersonate a google.com server even if they had access to the google.com TLS key. One may instantly and directly access any email box, file service, or cloud account using identity provider keys.

To secure important keys like this one, our industry, notably cloud service providers, must commit to higher security and transparency.

Which Applications Are Affected?

The analysis says the problem only affected Azure Active Directory applications that use Microsoft’s OpenID v2.0. Applications running on version 1.0 were unaffected since the token validation process did not use the compromised key.

Recommendation

• Search for the use of forged tokens and use the Indicators of Compromise (IoCs) published by Microsoft to look for any activity that originates from the IP addresses provided by Microsoft.
• Verify that no apps are using the cached version of the Microsoft OpenID public certificates, and clear the cache if they are.
• Microsoft has introduced extra verifications to the official Azure SDK to prevent the use of MSA keys to authenticate organization accounts. The most recent version of the package should be updated by users.

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