CVE-2026-27678: SAP S/4HANA Auth Bypass Vulnerability

CVE-2026-27678 Overview

CVE-2026-27678 is a Missing Authorization vulnerability (CWE-862) affecting the SAP S/4HANA backend OData Service, specifically the Manage Reference Structures component. Due to missing authorization checks, an authenticated attacker can update and delete child entities via exposed OData services without proper authorization, leading to unauthorized data modification.

Critical Impact

Attackers with low-privileged access can manipulate and delete reference structure data in SAP S/4HANA systems, compromising data integrity across enterprise operations.

Affected Products

• SAP S/4HANA (Manage Reference Structures OData Service)

Discovery Timeline

• April 14, 2026 - CVE-2026-27678 published to NVD
• April 14, 2026 - Last updated in NVD database

Technical Details for CVE-2026-27678

Vulnerability Analysis

This vulnerability stems from a Missing Authorization (CWE-862) weakness in the SAP S/4HANA backend OData Service responsible for managing reference structures. The OData Service exposes endpoints that allow interaction with child entities within reference structures, but fails to implement proper authorization checks before processing update and delete operations.

When an authenticated user sends a request to modify or remove child entities, the service processes the request based solely on authentication status without verifying whether the user has the appropriate authorization to perform the requested action on the specific entity. This architectural flaw allows any authenticated user to manipulate data they should not have access to, resulting in significant integrity impact.

The vulnerability specifically affects the integrity of data within reference structures while confidentiality and availability remain unaffected. This indicates that attackers cannot read unauthorized data or cause service disruption through this specific vulnerability, but can corrupt or delete critical business data.

Root Cause

The root cause is a missing authorization check in the SAP S/4HANA OData Service handling reference structure management. The service correctly authenticates incoming requests but fails to validate that the authenticated user has the necessary permissions to perform update or delete operations on the targeted child entities. This represents a classic broken access control pattern where authentication is present but authorization enforcement is absent.

Attack Vector

The attack vector is network-based, requiring the attacker to have low-privilege authenticated access to the SAP S/4HANA system. Once authenticated, the attacker can craft OData requests targeting the Manage Reference Structures service endpoints. By sending properly formatted HTTP PATCH or DELETE requests to the exposed OData endpoints, the attacker can modify or remove child entities within reference structures without possessing the appropriate authorizations.

The attack requires no user interaction and can be executed with low complexity. An attacker familiar with SAP OData service conventions can enumerate available endpoints and entities, then systematically target child entities for modification or deletion.

Detection Methods for CVE-2026-27678

Indicators of Compromise

• Unusual volume of UPDATE or DELETE operations on reference structure child entities from specific user accounts
• OData service requests targeting /sap/opu/odata/ endpoints for reference structure management from users without appropriate business roles
• Audit log entries showing modifications to reference structures by users who lack assigned authorization objects
• Unexpected changes to reference structure data that cannot be attributed to legitimate business processes

Detection Strategies

• Enable and monitor SAP Security Audit Log (SM21) for unauthorized access attempts to reference structure objects
• Implement SAP Read Access Logging (RAL) to track access patterns to sensitive OData services
• Configure SIEM integration to correlate authentication events with subsequent OData service calls for anomaly detection
• Review SAP Gateway logs for unusual patterns in HTTP methods (PATCH/DELETE) targeting affected services

Monitoring Recommendations

• Establish baseline activity patterns for the Manage Reference Structures OData Service and alert on deviations
• Monitor user activity reports in SAP GRC Access Control for users accessing reference structure functions without appropriate authorizations
• Implement real-time alerting for bulk modification or deletion operations on reference structure entities
• Conduct periodic reviews of authorization assignments for users with access to affected OData services

How to Mitigate CVE-2026-27678

Immediate Actions Required

• Apply the security patch documented in SAP Note #3715177 immediately
• Review and restrict access to the Manage Reference Structures OData Service to only authorized users
• Audit recent changes to reference structure data to identify potential unauthorized modifications
• Enable enhanced logging on affected OData services until the patch is applied

Patch Information

SAP has released an official security patch addressing this vulnerability. Organizations should reference SAP Note #3715177 for detailed patching instructions and prerequisites. The patch is also referenced in the SAP Security Patch Day Update. Apply this patch through your standard SAP maintenance process, ensuring proper testing in non-production environments before production deployment.

Workarounds

• Restrict network access to the affected OData service endpoints using SAP Gateway security configurations or firewall rules
• Implement additional authorization checks at the application layer using SAP Business Add-Ins (BAdIs) if available for the affected service
• Temporarily disable the Manage Reference Structures OData Service if it is not critical to business operations until patching is complete
• Apply principle of least privilege by reviewing and removing unnecessary user assignments to roles that grant access to reference structure management

# Review users with access to reference structure management
# Execute in SAP transaction SUIM to identify potentially affected users
# Path: User Information System > Users by Complex Selection Criteria
# Filter by authorization objects related to reference structure management