CVE-2026-40939: Data Sharing Framework Auth Bypass Flaw

CVE-2026-40939 Overview

CVE-2026-40939 is an Insufficient Session Expiration vulnerability (CWE-613) affecting the Data Sharing Framework (DSF), a distributed process engine implementing BPMN 2.0 and FHIR R4 standards. In versions prior to 2.1.0, OIDC-authenticated sessions lack a configured maximum inactivity timeout, allowing sessions to persist indefinitely after login even after the OIDC access token has expired. This session management flaw enables unauthorized access to protected resources if an attacker gains physical access to an authenticated user's device.

Critical Impact

Sessions persist indefinitely after OIDC token expiration, allowing prolonged unauthorized access through physical attack vectors on authenticated sessions.

Affected Products

• Data Sharing Framework (DSF) versions prior to 2.1.0
• DSF Business Process Engine (BPE) with OIDC authentication
• DSF FHIR server components with OIDC authentication

Discovery Timeline

• 2026-04-21 - CVE CVE-2026-40939 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-40939

Vulnerability Analysis

This vulnerability stems from improper session lifecycle management in the DSF framework's OIDC authentication implementation. When users authenticate via OIDC providers, the framework establishes a local session but fails to enforce session timeout policies. The attack requires physical access to an authenticated user's workstation or device, where an attacker can leverage the persistent session to access healthcare data and BPMN process workflows without re-authentication.

The vulnerability is particularly concerning in healthcare environments where DSF is deployed, as FHIR R4 resources may contain sensitive patient data. The lack of session expiration violates security best practices for session management and contradicts the expected behavior where sessions should be invalidated when underlying authentication tokens expire.

Root Cause

The root cause is the absence of a configured maximum inactivity timeout for OIDC-authenticated sessions in DSF versions before 2.1.0. The session management logic did not bind session validity to the underlying OIDC access token lifecycle, creating a disconnect between the identity provider's token expiration and the application's session state. This architectural oversight means that even after the OIDC access token expires, the local application session remains valid indefinitely.

Attack Vector

The attack vector requires physical access to a system with an authenticated DSF session. An attacker with physical access to an unlocked workstation can exploit the persistent session to:

1. Access FHIR R4 healthcare resources containing protected health information
2. Interact with BPMN 2.0 process workflows
3. Perform actions under the identity of the authenticated user
4. Maintain access even hours or days after the original authentication

The vulnerability exploits the gap between expected session behavior (timeout after inactivity) and actual behavior (indefinite persistence). Since no code examples are available, administrators should review the GitHub Security Advisory GHSA-gj7p-595x-qwf5 for technical implementation details and the specific configuration changes required.

Detection Methods for CVE-2026-40939

Indicators of Compromise

• Sessions active significantly longer than the configured OIDC token lifetime
• User activity occurring after OIDC access tokens have expired
• Unusual access patterns from workstations during off-hours or when users are known to be away
• Multiple actions performed under a single session over extended time periods without re-authentication

Detection Strategies

• Implement session duration logging and alert on sessions exceeding expected OIDC token lifetimes
• Correlate DSF session activity with OIDC provider token expiration events
• Monitor for access to FHIR resources outside normal business hours from previously authenticated sessions
• Review access logs for sessions that remain active for unusually long periods

Monitoring Recommendations

• Enable comprehensive session lifecycle logging in DSF BPE and FHIR components
• Configure SIEM rules to detect sessions persisting beyond OIDC token expiration windows
• Implement user behavior analytics to identify anomalous access patterns from persistent sessions
• Periodically audit active sessions and compare against expected authentication windows

How to Mitigate CVE-2026-40939

Immediate Actions Required

• Upgrade DSF installations to version 2.1.0 or later immediately
• Terminate all existing active sessions after the upgrade to force re-authentication
• Review session logs for evidence of exploitation prior to patching
• Implement physical security controls for workstations accessing DSF systems

Patch Information

The vulnerability is fixed in DSF version 2.1.0. The fix implements proper session timeout configuration for OIDC-authenticated sessions. The patch is available via GitHub Commit f4ecb002. Detailed OIDC configuration guidance for the patched version is available in the DSF OIDC Operations Documentation for BPE and the DSF FHIR Operations Documentation for FHIR components.

Workarounds

• Implement automatic screen lock policies on workstations accessing DSF to reduce physical access risk
• Configure network-level session timeouts or reverse proxy session limits as a defense-in-depth measure
• Require periodic re-authentication for sensitive FHIR resource access through application-level controls
• Enforce strict physical access controls in areas where DSF-authenticated workstations are located

# Upgrade DSF to patched version 2.1.0
# After upgrade, invalidate all existing sessions to ensure proper timeout behavior
# Refer to vendor documentation for specific configuration steps:
# BPE: https://dsf.dev/operations/v2.1.0/bpe/oidc.html
# FHIR: https://dsf.dev/operations/v2.1.0/fhir/oidc.html