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The Silent Threat Inside Entra’s Identity System
A newly revealed vulnerability dubbed nOAuth is sounding alarms across the cybersecurity world, particularly within Microsoft’s Entra ecosystem. This critical flaw exposes SaaS applications to the risk of full account takeover due to a widespread misimplementation of OpenID Connect (OIDC) protocols. By exploiting Entra’s handling of unverified email attributes, malicious actors can impersonate users across tenant boundaries without triggering standard security defenses. The vulnerability has laid bare how improper identity handling can create systemic threats, especially in complex multi-tenant cloud environments.
As SaaS adoption continues to surge, this discovery spotlights the urgent need for stronger adherence to identity standards and deeper scrutiny of application-level authentication logic. While Microsoft has taken partial steps to tighten the default behavior in Entra ID, the responsibility still lies largely with application developers, whose misconfigurations are the root cause of this issue. With detection almost impossible using traditional methods and the impact involving sensitive data and services tied to Microsoft 365, nOAuth is a ticking time bomb that demands immediate attention.
Alarming Exploit Reveals Identity Missteps in SaaS Ecosystems
How nOAuth Works
The core of the nOAuth vulnerability lies in the misuse of the email claim as a unique user identifier in SaaS applications. Instead of relying on the recommended issuer (iss) and subject (sub) pair to authenticate users as prescribed by OIDC standards, many developers opt to use mutable, user-controlled email addresses. This opens the door for attackers to exploit Microsoft Entra ID, which allows users to assign unverified email addresses in their tenant accounts.
Attack Execution
With just the knowledge of a victim’s email address and access to a separate Entra tenant, an attacker can register a new user account mimicking the email of the victim. If the targeted SaaS app uses email to authenticate, the attacker bypasses authentication entirely and gains full access to the victim’s data. No need for complex hacking or phishing—the trust the app places in the email claim is enough.
Real-World Risk
In a detailed study conducted by the Semperis Security Research Team, 104 SaaS applications in Microsoft’s Entra App Gallery were tested. Shockingly, 9% were vulnerable to nOAuth, including services holding sensitive personal data and those integrated with Microsoft 365. These figures underscore the widespread nature of this design flaw.
Why Detection Fails
Conventional defenses like MFA, EDR, and conditional access offer no protection because the authentication request appears legitimate. The attack doesn’t circumvent Microsoft’s security mechanisms—it abuses the application’s internal trust model. Even advanced SaaS Security Posture Management (SSPM) tools fall short, as they primarily monitor configurations, not runtime behavior.
Microsoft’s Response
Microsoft has taken some steps to mitigate the issue:
Updated default behavior: New Entra app registrations no longer emit unverified email claims unless explicitly set.
New xms_edov claim: This optional marker helps flag unverified emails—but only if developers use it properly.
However, these changes don’t fix the thousands of apps built before the update. Worse, most SaaS providers haven’t yet implemented the new protections or moved away from using email claims.
Developer Burden
The only true fix is for developers to stop using email addresses as identity anchors. Instead, they must follow OIDC best practices, using the immutable iss + sub combination and robust email verification flows. For apps supporting identity federation or account merging, these safeguards are critical.
What Users Can Do
Unfortunately, customers have very limited recourse. They can:
Pressure vendors to patch the flaw
Cease using vulnerable apps
Attempt highly complex log correlation across Entra ID and SaaS app logs—though this is rarely feasible
Industry Call to Action
With coordination from Microsoft, Semperis disclosed the vulnerability to affected vendors. But the persistence of at-risk applications underscores a systemic issue in cloud app development: a lack of identity discipline. As organizations race toward SaaS adoption, nOAuth is a wake-up call that secure identity handling is not optional—it’s foundational.
What Undercode Say:
Root Cause: Trusting the Untrustworthy
The nOAuth flaw doesn’t exploit a bug—it exploits developer assumptions. Many SaaS developers wrongly assume that an email address is a reliable identity attribute, especially in the Microsoft Entra environment. But in reality, email is mutable, unverified by default, and easily spoofed across tenants. This is a textbook example of poor identity hygiene leading to catastrophic results.
The Myth of Email as Identity
Using email as a unique identifier is a convenience trap. It simplifies login and user management but sacrifices security. Developers often choose it because it’s familiar, easy to implement, and works across identity providers. But ease of use has now opened the door to full account takeover—a cost far greater than the convenience it offers.
Why SaaS Security Posture Management
SSPM tools focus heavily on configuration, not authentication flow monitoring. They flag misconfigured access controls or excessive privileges but can’t see an attacker registering a duplicate email in another tenant and slipping past the front door. What’s needed is runtime validation—monitoring actual login events and comparing them to a known user fingerprint.
Detection Complexity
Even when defenders know what to look for, they face major hurdles. Logs from Entra ID and SaaS apps are often incompatible, incomplete, or missing crucial identifiers. Stitching them together requires custom scripts, a mature SIEM setup, and luck. That’s far beyond what most IT teams can afford to do at scale.
Microsoft’s Limited Safeguards
While Microsoft’s updates to Entra are a step in the right direction, they don’t go far enough. Most legacy apps won’t adopt the xms_edov claim or switch identity logic unless forced. And Microsoft’s threat of removal from the Entra App Gallery may still not be enough to drive meaningful change, especially for smaller vendors with low visibility.
Developer Responsibility Is the Bottleneck
nOAuth’s resolution hinges on developer behavior, which is notoriously hard to enforce at scale. Some may not even be aware they’re vulnerable. Others may delay fixing the issue due to lack of resources, prioritization, or understanding. Unless there is a community-wide push, including customer pressure and vendor audits, the status quo is likely to persist.
Implications for Zero Trust
This vulnerability directly undermines Zero Trust principles, which assume breach and verify every identity. By allowing email-based impersonation, nOAuth shows how misconfigured apps can silently break trust models without violating core IAM policies. It’s a powerful reminder that Zero Trust isn’t just about infrastructure—it’s also about app logic.
Looking Ahead
With cloud-first strategies dominating IT roadmaps, the security community must address identity flaws at the application level. Education, threat modeling, and updated SDKs must all be part of the solution. Enterprises should prioritize vendor transparency around identity handling and factor it into procurement decisions.
🔍 Fact Checker Results:
✅ The nOAuth flaw is real and confirmed by security research from Semperis and Microsoft
❌ Traditional security tools like MFA and EDR do not protect against this attack
✅ Microsoft has made default changes, but legacy apps remain vulnerable
📊 Prediction:
🔐 Expect increased scrutiny of identity practices in SaaS apps throughout 2025
🚨 Vendors who fail to fix nOAuth could face public exposure or delisting from trusted directories
📈 Demand for real-time identity validation and app-level runtime monitoring will rise across regulated industries
References:
Reported By: cyberpress.org
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