Microsoft Vulnerability Severity Classification for Online Services

Our commitment to protecting customers from vulnerabilities in our software, services, and devices includes providing security updates and guidance that address those vulnerabilities when they are reported to Microsoft. We want to be transparent with our customers and security researchers in our approach. The following table describes the Microsoft data classification and severity for common vulnerability types for online services or web applications. It is derived from the Microsoft Security Response Center (MSRC) advisory rating. The MSRC uses this information to triage bugs and determine severity. To provide the best protection for our customers, we always prioritize fixing important and critical severity issues.

Data classification in the context of this document pertains to the data hosted on or by the service and its exposure through the identified vulnerability. The severity of the vulnerability is determined by the impact of the data that could be accessed. In addition, the ease of exploitation is also considered during severity assessment.

Microsoft Vulnerability Severity Classification for Online Services

Vulnerability Type	Data Classification	Severity	Example (For reference only)
Cross Site Scripting (XSS)	Highly Confidential	Critical	XSS that can compromise user session tokens or sensitive cookies with no victim interaction or actions required
	Confidential	Important	XSS that can compromise user session tokens or sensitive cookies
	General	Moderate	XSS triggering on public pages that does not disclose private data or allow the compromise of an authenticated session
	Public	Low	XSS requiring a victim to input the malicious code themselves
Authentication Issues	Highly Confidential	Critical	Vulnerability allowing attacker to authenticate as another highly privileged user or cross tenant without victim’s interaction
	Confidential	Important	Vulnerability allowing authenticated attacker within a tenant to elevate their privilege
	General	N/A	Read only access to a web directory that should be authenticated, like a directory that contains generic images for an internal only site, but no sensitive information is obtainable
	Public
Improper Access Control	Highly Confidential	Critical	Missing access controls exposes sensitive data from another customer
	Confidential	Important	An unprivileged user accessing data intended for privileged user
	General	Moderate	An unprivileged user viewing non-sensitive data without permission
	Public	Low	An unprivileged user viewing non-sensitive data that’s not intended to be public
Injection (SQL injection and Command injection)	Highly Confidential	Critical	Injection leading to elevation of privilege to a different tenant
	Confidential	Important	Injection leading to elevation of privilege in the same tenant
	General
	Public	Moderate	Blind SQL Injection with no sensitive information disclosed
Cross-Site Request Forgery (CSRF)	Highly Confidential	Critical	CSRF vulnerability performing highly privileged administrative action, like allowing account credential reset on any user in an Azure service
	Confidential	Important	CSRF vulnerability resulting in the change of a user’s email address and subsequent account takeover
	General	Moderate	CSRF vulnerability allowing a minor change to an users account, like adding a personal note to a user’s account
	Public	Low	A CSRF vulnerability on an unauthenticated form
Server-Side Request Forgery (SSRF)	Highly Confidential	Critical	Cross tenant information disclosure or elevation of privilege after reaching internal servers
	Confidential	Important	SSRF vulnerability sending requests to sensitive internal endpoints that leaks sensitive information or performs a sensitive action
	General	Moderate	Blind SSRF reaching ports that should not be open
	Public	Low	Blind SSRF that is only used for port scanning
Deserialization of Untrusted Data	Highly Confidential	Critical	Deserialization leading to unauthenticated cross tenant remote code execution
	Confidential	Important	Deserialization leading to compromise of a system that processes data belonging to the current user
	General	Moderate	Deserialization leading to Server Denial of Service
	Public	Low	Deserialization triggering only an HTTP 500 error with no other impact to the system
Web Security Misconfiguration	Highly Confidential	Critical	Default admin credentials that access an important resource
	Confidential	Important	URL redirect in an OAuth flow that leaks the OAuth token
	General	Low	Clickjacking due to lack of the X-FRAME-OPTIONS response header or lack of frame-ancestors in a CSP
	Public	Low	Missing length check on web app form leading to denial of service for the user, requiring them to refresh the page
Cross Origin Access Issues	Highly Confidential	Critical	Improper CORS (trusted origin) validation leading to disclosure of tokens with excessive permissions
	Confidential	Important	Improper CORS (trusted origin) validation
	General	Moderate	Access-Control-Allow-Origin header in response reflecting any value put in Origin header in the request, along with Access-Control-Allow-Credentials being set to true
	Public	Low	Access-Control-Allow-Origin header in the response has been set to ‘*’ with no additional exploitation
Improper Input Validation	Highly Confidential	Critical	Tampering with request parameters affects the application’s logic and allows for cross tenant information exposure, privilege escalation
	Confidential	Important	Changing a parameter’s value affects the application’s logic, resulting in an exposure of sensitive information or allows the user to perform a sensitive action
	General	Moderate	Tampering with input parameters that can only cause visual cosmetic changes to the user interface
	Public	Low	Modifying input parameters that make the user interface difficult to use

Serverity Example for User Enumeration:

Important Severity: If the target had no rate limitation or no logging.
Moderate Severity: Username and/or email address leak via external API.

Microsoft recognizes that this list may not incorporate all online service vulnerability types and new vulnerabilities that may be discovered at any time. Some denial of service vulnerabilities that require low attacker resources may be serviced after a case-by-case evaluation. We reserve the right to classify any vulnerabilities that are not covered by this document at our discretion.

Data Classification

The following table outlines Microsoft’s general data classification guidelines. There may be exceptions and modifications made on a case-by-case basis at our discretion.

Data Classification	Description	Examples
Highly Confidential	The most critical data owned, used, and managed by the business. This very sensitive data requires the strictest protection available. Inappropriate disclosure, modification, or destruction of this data would result in significant business harm to the business or its shareholders, partners, or customers.	Payment data Customer data Future or active sales and marketing plans Software tokens
Confidential	Sensitive business data owned, used, and managed by the business. Inappropriate disclosure, modification, or destruction of this data would result in moderate business harm to the business or its shareholders, partners, or customers.	Confidential source code Media product features and release schedule Business account data
General	Business data that is not meant for public consumption.	Zip code (not associated with an individual) Media assets that can be viewed by anyone under NDA. Real-time-geo-location data
Public	Data designed for public consumption.	Open source code Announced financial reports Approved public video