CVE-2026-89105: SAP Cloud Security Auth Bypass Flaw

CVE-2026-89105 Overview

CVE-2026-89105 affects the HybridTokenAuthenticator component of the SAP cloud-security-services-integration-library. The component accepts tokens from unintended ambient Identity Authentication Service (IAS) and Extended Services for User Account and Authentication (XSUAA) bindings. Attackers can present tokens that should be rejected and gain unauthorized access to protected resources. The flaw is tracked under CWE-1188: Initialization of a Resource with an Insecure Default and is categorized as an authentication and trust boundary issue.

Critical Impact
Attackers with low privileges can leverage ambient service bindings to authenticate with tokens outside the intended trust boundary, resulting in limited confidentiality and integrity impact.

Affected Products

SAP cloud-security-services-integration-library (HybridTokenAuthenticator component)
Applications integrating with SAP Identity Authentication Service (IAS)
Applications integrating with SAP XSUAA (Extended Services for User Account and Authentication)

Discovery Timeline

2026-10-13 - CVE-2026-89105 published to the National Vulnerability Database
2026-10-15 - Last updated in NVD database

Technical Details for CVE-2026-89105

Vulnerability Analysis

The HybridTokenAuthenticator validates JSON Web Tokens (JWTs) issued by SAP identity providers. In vulnerable versions, the authenticator does not strictly bind token validation to the intended service binding. When multiple IAS or XSUAA bindings are present in the application's runtime environment, the authenticator may accept tokens issued for a different ambient binding than the one the application expects.

This weakens the trust boundary between tenants and service instances. An attacker holding a token valid for one ambient binding can present it to an application that should only accept tokens from a different binding. The attack requires network access and low privileges, and succeeds under constrained conditions that raise attack complexity.

Root Cause

The root cause maps to [CWE-1188], which describes initialization of a resource with an insecure default. The HybridTokenAuthenticator enumerates available service bindings and treats any valid token from those bindings as acceptable, rather than restricting validation to the specific binding configured for the protected resource. Token issuer, audience, and binding identifier are not enforced together as a single trust tuple.

Attack Vector

An attacker needs a valid token from any ambient IAS or XSUAA binding that the target application can observe at runtime. The attacker submits the token to the target application over the network. The HybridTokenAuthenticator validates the signature and standard claims, finds a matching ambient binding, and grants access. Exploitation requires specific environmental conditions, including co-located bindings and tokens the attacker can legitimately obtain.

See the GitHub Security Advisory GHSA-857v-p42q-f3qf for component-level technical details.

Detection Methods for CVE-2026-89105

Indicators of Compromise

Successful authentication events where the token issuer or audience claim does not match the application's configured service binding identifier.
Access tokens validated against an IAS or XSUAA binding other than the one associated with the requested resource.
Unexpected tenant identifiers (zid, ext_attr.zdn) appearing in authenticated sessions.

Detection Strategies

Review application logs for authentication decisions by HybridTokenAuthenticator and correlate the accepted token's binding with the resource being accessed.
Enable verbose logging in the SAP cloud security library to capture which service binding was used to validate each incoming token.
Audit SAP Business Technology Platform (BTP) service bindings bound to each application instance and flag applications that hold more than one IAS or XSUAA binding.

Monitoring Recommendations

Monitor for authentication requests from clients whose source network or tenant does not align with the application's intended user population.
Alert on sessions where the authenticated principal belongs to a tenant not expected by the protected service.
Track the version of cloud-security-services-integration-library deployed across workloads and flag versions prior to the fixed release.

How to Mitigate CVE-2026-89105

Immediate Actions Required

Upgrade the SAP cloud-security-services-integration-library to the patched version listed in the vendor advisory.
Inventory all applications using HybridTokenAuthenticator and identify those bound to multiple IAS or XSUAA service instances.
Rotate any service credentials or signing keys that may have been exposed through unintended ambient bindings.

Patch Information

SAP has issued a fix as part of its security patch day release. Refer to the GitHub Security Advisory GHSA-857v-p42q-f3qf for the fixed version range and to the SAP Security Patch Day announcement for the corresponding SAP Security Note.

Workarounds

Remove unnecessary IAS or XSUAA service bindings from applications so that only the intended binding is present at runtime.
Explicitly configure the authenticator with the expected service binding identifier where the library supports binding pinning.
Segregate applications with different trust requirements into separate deployment units to eliminate ambient binding overlap.

bash

# Configuration example: inventory bindings on an SAP BTP Cloud Foundry application
cf env <app-name> | grep -E "identity|xsuaa"

# Unbind unintended service instances to remove ambient trust
cf unbind-service <app-name> <unintended-identity-or-xsuaa-instance>
cf restage <app-name>