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  • Vishal Masih

Reevaluating Our Dependence on Microsoft: May Be It’s Time to Diversify

Updated: May 2

Today Microsoft is everywhere. Active Directory was the enterprise infrastructure backbone once, and still is. However, our dependence on Microsoft has grown ever more as the company has released new product offerings, including hardware and software, covering almost all areas of enterprise IT. They are now the de facto standard for enterprise email, communication, and collaboration for organizations of all sizes. And now they are becoming the staple for enterprise security, device management and business intelligence too. All this, besides being the number two CSP.

I personally like the Microsoft 365 set of products too. The convenience of one suite to bundle your M365 email, Office 365, Defender for endpoint, device, and cloud, etc. is very appealing. You can consolidate the necessities you need to run your business in one product suite and call it a day. Long story short, we have enjoyed the convenience and user-friendliness of the M365 suite.

However, because Microsoft is everywhere, they have become the target of choice for everyone. And Microsoft is not setting a great example here. With that in mind, I am writing this blog.

The CISA CSRB Report on the Microsoft Attack

We are a cybersecurity provider. And personally, given a choice between security and convenience, I will always pick security, but that’s just me. However, the landscape is changing, and the consequences are significant. We are not just talking about petty thieves anymore. There are nation state actors actively conducting cyber espionage and warfare. There’ a “Cyber Cold War” going on and from the likes of it, we are not doing that great. So yes, a little inconvenience is a small price to pay in the larger scheme of things.

In April 2024, CISA released the CSRB review of the successful attack on Microsoft Exchange Online that was carried out in the summer of 2023 by Storm-0558, a Chinese APT. It is a short 34 page read, available here: I would recommend ever cybersecurity professional to read it.

Well, to start with I commend the work the CSRB did and CISA for releasing the report. And a  big thank you to all contributors and even Microsoft for cooperating completely and openly with the CSRB.

And that is where my commendation for Microsoft stops. Here are a few excerpts from the CISA CSRB report (I am quoting the report verbatim):

  • The Board concludes that this intrusion should never have happened. Storm-0558 was able to succeed because of a cascade of security failures at Microsoft, as outlined in this report.

  • In May and June 2023, a threat actor compromised the Microsoft Exchange Online mailboxes of 22 organizations and over 500 individuals around the world.

  • In fact, when combined with another flaw in Microsoft’s authentication system, the key permitted Storm-0558 to gain full access to essentially any Exchange Online account anywhere in the world.

  • Observation: "Microsoft’s failure to detect the compromise of its cryptographic crown jewels on its own, relying instead on a customer to reach out to identify anomalies the customer had observed"

  • Once the State Department alerted Microsoft to the intrusion, Microsoft did not have the logs or other forensic data to determine how or when Storm-0558 had stolen the key.

  • As of the date of this report, Microsoft does not know how or when Storm-0558 obtained the signing key.

  • The Board identified a series of Microsoft operational and strategic decisions that collectively point to a corporate culture that de-prioritized both enterprise security investments and rigorous risk management.

  • The loss of a signing key is a serious problem, but the loss of a signing key through unknown means is far more significant because it means that the victim company does not know how its systems were infiltrated and whether the relevant vulnerabilities have been closed off.

  • The Board is convinced that Microsoft should address its security culture.


In fact, when combined with another flaw in Microsoft’s authentication system, the key permitted Storm-0558 to gain full access to essentially any Exchange Online account anywhere in the world.

And this is just a snapshot from the report. I will go into the details below.

How it Happened

Storm-0558 Token Abuse Attack on Microsoft Summer 2023 (Courtsey: CISA CSRB)
Storm-0558 Token Abuse Attack on Microsoft Summer 2023 (Courtesy: CISA CSRB)

From the CSRB:

“On June 26, 2023, Microsoft discovered that the threat actor had used OWA to access emails directly using tokens that authenticated Storm-0558 as valid users. Such tokens should only come from Microsoft’s identity system, yet these had not. Moreover, tokens used by the threat actor had been digitally signed with a Microsoft Services Account (MSA) cryptographic key that Microsoft had issued in 2016. This particular MSA key should only have been able to sign tokens that worked in consumer OWA, not Enterprise Exchange Online. Finally, this 2016 MSA key was originally intended to be retired in March 2021, but its removal was delayed due to unforeseen challenges associated with hardening the consumer key systems. This was the moment that Microsoft realized it had major, overlapping problems: first, someone was using a Microsoft signing key to issue their own tokens; second, the 2016 MSA key in question was no longer supposed to be signing new tokens; and third, someone was using these consumer key-signed tokens to gain access to enterprise email accounts.”

Those are 3 strikes if you ask me!

How It Could Have Been Prevented

Again, this is from the CSRB:

  • If Microsoft:

    • had not paused manual rotation of keys;

    • had completed the migration of its MSA environment to rotate keys automatically;

    • had put in place a technical or other control to generate alerts for aging keys,

    • the 2016 MSA key would not have been valid in 2023.

  • Further, if Microsoft had not made the error that allowed consumer keys to authenticate to enterprise customer data (or, alternatively, if it had detected and addressed this flaw), the scope of the intrusion would have been far narrower and would not have impacted the State Department, Commerce Department, or any other enterprise customers.

  • If Microsoft had deployed alerting or prevention to detect forged tokens that do not conform to Microsoft’s own token generation algorithms, this incident likely could also have been stopped or detected by Microsoft all on its own.

  • Even after all this, if Microsoft had other security controls in place for its digital identity system—as the Board finds other CSPs had in place at the time—this intrusion vector could have been blocked or detected.

What Makes This Worse

This quote sums up the problem at Microsoft:

The decision to completely stop manual rotation of signing keys in 2021 after a large cloud outage, along with failing to prioritize the development of an automated key rotation solution, are troubling examples of decision-making processes within the company that did not prioritize security risk management at a level commensurate with the threat and with Microsoft technology’s vital importance to more than one billion of its customers worldwide.

And I always wondered why I need to pay extra for security logging. I am already trusting your environment and you with my IP and confidential data, and paying you a decent amount for it, why do I need to pay extra to check if my trust is unfounded or not. The CSRB has similar thoughts:

“The Board notes that some CSPs, including Microsoft until recently, offer granular logging, which can be invaluable in security incident detection, investigation, and response—as a part of a paid package offering to their core services. This course of business should stop. Security-related logging should be a core element of cloud offerings and CSPs should provide customers the foundational tools that provide them with the information necessary to detect, prevent, or quantify an intrusion, recognizing that many customers will still require additional or third-party analytic capabilities to build a fully mature security program”.

Compared To AWS, GCP and OCI

We are not an avid AWS or GCP user internally and have not used OCI yet. So the CSRB's comments on how these CSPs do things differently is a welcome insight:


"Google re-worked its identity system to rely as much as possible on stateful tokens, in which every credential is assigned a unique identifier at issuance and recorded in a database as irreversible proof that the credential Google receives is one that it had issued. Google also implemented fully automatic key rotation where possible and tightened the validation period for stateless tokens, reducing the window of time for threat actors to locate and obtain active keys. Google also undertook a comprehensive overhaul of its infrastructure security including implementing Zero Trust networks and hardware-backed, Fast IDentity Online (FIDO)-compliant two-factor authentication (2FA) to protect these identity systems."


"Similarly, the Amazon Web Services (AWS) IAM Signature Version 4 (SigV4) protocol provides each customer with unique authentication keys for each of their users or roles, but these keys are not bearer tokens nor are they used directly for signing. Having no tokens, these credentials are not susceptible to token replay. Instead, highly compartmentalized signing keys are cryptography-derived, and each request is signed in a way that can only authorize the same specific action, which can be safely retried."


"Oracle Cloud Infrastructure also enables and requires each customer tenancy to have its own public-private key pair that signs each request sent on an encrypted Transport Layer Security (TLS) connection, in a token spoofing-resistant manner."

CSRB’s Recommendations for Microsoft

These are recommendations the CSRB provided Microsoft and I would have expected Microsoft to already have these in place:

  • Per customer keys (key scope): Microsoft had a single key that signed tokens for all consumer, and due to the validation flaw, enterprise customers. Tying encryption keys to customer tenancy would limit the scope of key compromise.

  • Bound tokens: Microsoft’s identity system used bearer tokens that did not require any proof of possession, thus making the tokens more vulnerable to replay attacks. By digitally binding tokens to specific requests or network sessions, token theft and token replay attacks can be eliminated. While this incident demonstrates the risks of key compromise, some victims and responders spent significant time investigating bearer token replay attacks to which not all CSPs are vulnerable.

  • Common authentication libraries: Microsoft used a variety of different client libraries to verify tokens across different systems. This diversity complicated implementing uniform, and correct, validation behavior, as well as made the remediation efforts much more complex and time sensitive. By ensuring that all CSP services use the same authentication libraries, CSPs can more effectively enforce consistent token validation behavior and authorization policy.

  • Secure key storage: While Microsoft separated the organization and production environments, this incident illustrated that Microsoft insufficiently protected MSA system key material. By storing key material in isolated systems and leveraging, where feasible, technologies such as dedicated HSMs, the risk of key compromise can be reduced.

  • Linkable tokens: The relationship between the tokens used in this incident was not exposed in logs made available to customers, making them difficult to track. By linking all tokens derived from a single root authentication event together and exposing this linking to their customers in logs, CSPs and customers can better track and discover identity-related attacks and respond, including in an automated way.

  • Proprietary data use in token generation algorithm: Some CSPs inject proprietary data into their generated authentication tokens, which they can use to differentiate between tokens that their own systems generated and those generated by malicious third parties. While one cannot rely on the fact that the adversary would not detect and reproduce such behavior, it can nevertheless prove potentially helpful as a “canary in the coal mine” alert that the CSP is observing tokens that had not been generated by its own code.

  • CSPs should implement emerging standards such as Open Authorization (OAuth) 2 Demonstrating Proof-of-Possession (DPoP) (bound tokens) and OpenID Shared Signals and Events (SSE) (sharing session risk) that better secure cloud services against credential related attacks.

But Wait There's More

After the cyberattack carried out by Storm-0558 in May-June 2023, Microsoft ended up being a victim of another state-sponsored group. This time it was Midnight Blizzard, the Russian state-sponsored actor also known as NOBELIUM. Here's the response from MSRC:

This time the attackers used password spraying to get access to a legacy OAuth application in a test tenant which had excessive privileges to the Microsoft corporate environment. That allowed the attackers to gain access to email accounts of senior high ranking officers from within Microsoft. The target was email correspondence between Federal Civilian Executive Branch (FCEB) agencies and Microsoft. Besides, the email the hackers accessed company’s source code repositories and internal systems.

As per this CISA directive, , and Microsoft's own blog, Midnight Blizzard is still using information initially exfiltrated from the corporate email systems, including authentication details shared between Microsoft customers and Microsoft by email, to gain, or attempt to gain, additional access to Microsoft customer systems.

Midnight Blizzard’s successful compromise of Microsoft corporate email accounts and the exfiltration of correspondence between agencies and Microsoft presents a grave and unacceptable risk to agencies. - CISA Emergency Directive (ED 24-02: Mitigating the Significant Risk from Nation-State Compromise of Microsoft Corporate Email System)

Reevaluating Our Dependence on Microsoft

We are a Microsoft shop and so is most of the corporate world. And therein lies the problem.

Because Microsoft is so ubiquitous, so entrenched in our organizational IT infrastructure, it has become the biggest target for these state-sponsored attackers.

We on the other hand, have become too complacent. M365 is everywhere. There's so much reliance on it that we have become borderline apathetic to such breaches. We say "it is not a question of if, but when". "Another day, another breach".

However, the question we must ask is, what are we doing as consumers, to make a difference. May be I am being naive, overreacting even, but I was hoping Microsoft, with its billions of dollars and thousands of engineers, would have been able to better stand up to this challenge.

Having said all that, I am now thinking that may be consolidation isn't a good strategy anymore. May be defense in depth means we don't put all our eggs in the same basket. May be, and I know it is going to be painful for almost all organizations, it’s time that we rethink our software stack, and diversify. Use different tools and different providers for different purposes. And not use a single identity stack if that stack can be compromised from within.

And may be it is time to reevaluate our dependence on Microsoft.

I don't have the definite answers to these questions. But I know that during this Memorial Day 2024 weekend, we will be moving from M365 to Google workspace. I am not saying Google workspace won't be successfully attacked ever, but at least going by the record of recent events, it is far less likely to happen.

The migration will be a pain. We will miss the ease of collaborating with our partners, clients and vendors who mostly use the M365 suite. And we will still need to buy Office 365 application licenses. In fact, I am writing this article on Microsoft Word.

However, I believe it’s time to take the path less taken.

We are a technology company, we always figure it out, and this time too we will find a way to make it work.

M365, we will miss you and wish you the best. May be our paths will cross again.



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