CVE-2026-49159: Microsoft Graph Information Disclosure Flaw

CVE-2026-49159 Overview

CVE-2026-49159 is an information disclosure vulnerability in Microsoft Graph. An authorized attacker with low-level privileges can retrieve sensitive information over a network. The flaw is categorized under [CWE-200] Exposure of Sensitive Information to an Unauthorized Actor.

Microsoft Graph is the unified API endpoint that provides access to Microsoft 365 data, including users, groups, mail, calendars, and files. A weakness in access mediation permits authenticated callers to view data they should not be entitled to read. The vulnerability affects confidentiality only, with no impact on integrity or availability.

Critical Impact
Authenticated attackers can disclose sensitive tenant data through Microsoft Graph API calls without requiring user interaction.

Affected Products

Microsoft Graph (cloud service)
Applications and tenants consuming Microsoft Graph APIs
Microsoft 365 environments integrated with Graph endpoints

Discovery Timeline

2026-07-24 - CVE-2026-49159 published to the National Vulnerability Database
2026-07-29 - Last updated in NVD database

Technical Details for CVE-2026-49159

Vulnerability Analysis

CVE-2026-49159 stems from improper enforcement of authorization boundaries within Microsoft Graph. The service returns data to authenticated principals whose scopes or role assignments should not grant visibility into the requested objects. Because Microsoft Graph aggregates identity, mail, files, and directory data, a single missing check can expose multiple content types.

The attack requires network access and valid credentials with limited privileges. No user interaction is needed to trigger the disclosure. Successful exploitation compromises confidentiality of tenant data while leaving system integrity and availability intact.

Root Cause

The vulnerability originates from insufficient access control checks on Microsoft Graph API responses. A property, relationship, or endpoint returns data without validating whether the calling principal holds the required delegated or application permission. This class of flaw maps to [CWE-200], where sensitive information reaches an actor outside the intended trust boundary.

Attack Vector

An attacker authenticates to the target Microsoft Graph tenant using stolen, phished, or legitimately obtained low-privilege credentials. The attacker then issues crafted HTTPS requests to Microsoft Graph endpoints. The service returns records that the attacker's assigned scopes should not authorize. Because the exploit uses standard Graph API calls, the traffic blends into normal application telemetry.

Microsoft has addressed the vulnerability as a cloud service update. Consult the Microsoft Security Update Guide CVE-2026-49159 for the authoritative advisory. No public proof-of-concept code is available at the time of publication, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-49159

Indicators of Compromise

Unusual volumes of Microsoft Graph API calls from a single service principal or user account
Graph requests targeting endpoints outside the caller's typical usage pattern, such as /users, /messages, or /drives
Access tokens issued to low-privilege identities generating high-cardinality read operations
Sign-ins from anomalous locations or infrastructure immediately preceding elevated Graph query activity

Detection Strategies

Baseline normal Microsoft Graph consumption per application, service principal, and user, then alert on statistical deviations
Correlate Microsoft Entra ID sign-in logs with Graph audit logs to identify tokens used from unexpected sources
Hunt for enumeration patterns such as sequential $select, $expand, or $top parameters that indicate bulk data harvesting

Monitoring Recommendations

Enable Microsoft Purview audit logging and forward Graph activity to a centralized analytics platform for retention and correlation
Review OAuth consent grants and application permissions weekly to identify overprivileged scopes
Track token issuance for service principals and alert when dormant identities suddenly issue Graph queries

How to Mitigate CVE-2026-49159

Immediate Actions Required

Confirm the Microsoft Graph service-side fix is in effect by reviewing the Microsoft Security Update Guide CVE-2026-49159
Audit application registrations and service principals for excessive delegated or application permissions on Microsoft Graph
Rotate credentials and secrets for any service principal suspected of unauthorized Graph queries
Enforce Conditional Access policies that require compliant devices and managed locations for Graph-consuming applications

Patch Information

Microsoft Graph is a cloud service, and Microsoft applies fixes at the service layer without customer action. The advisory at Microsoft Security Update Guide CVE-2026-49159 documents the remediation and any tenant-side hardening steps. Verify that dependent applications continue to function as expected after Microsoft deploys the update.

Workarounds

Apply least-privilege scoping to all Graph API permissions and remove unused delegated grants
Restrict Graph access using Conditional Access, IP-based location policies, and Continuous Access Evaluation
Enable Microsoft Entra ID Privileged Identity Management for administrative roles that interact with Graph

bash

# Example: enumerate Graph API permissions granted to enterprise applications
Get-MgServicePrincipal -All | ForEach-Object {
    Get-MgServicePrincipalOAuth2PermissionGrant -ServicePrincipalId $_.Id |
        Select-Object ClientId, ConsentType, Scope
}