CVE-2026-40942 Overview
The Data Sharing Framework (DSF), a distributed process engine based on BPMN 2.0 and FHIR R4 standards, contains a critical logic error in its OIDC caching mechanism. Prior to version 2.1.0, the framework implements an inverted time comparison in multiple cache components, using isBefore instead of isAfter for timestamp validation. This fundamental logic flaw creates two distinct security issues: the OIDC JWKS and Metadata Document caches never return cached values (causing excessive HTTP requests to the OIDC provider), while the OIDC token cache for FHIR client connections never invalidates (returning expired tokens indefinitely).
Critical Impact
This vulnerability can lead to denial of service through resource exhaustion due to excessive HTTP requests, and potential security bypass through the continued use of expired authentication tokens.
Affected Products
- Data Sharing Framework (DSF) versions prior to 2.1.0
- DSF deployments utilizing OIDC authentication with FHIR R4 integrations
- Healthcare data sharing systems built on DSF infrastructure
Discovery Timeline
- 2026-04-21 - CVE CVE-2026-40942 published to NVD
- 2026-04-22 - Last updated in NVD database
Technical Details for CVE-2026-40942
Vulnerability Analysis
This vulnerability falls under CWE-670 (Always-Incorrect Control Flow Implementation), representing a fundamental logic error in conditional time-based cache validation. The DSF framework's caching layer contains two separate but related flaws stemming from the same root cause: an inverted boolean condition in timestamp comparisons.
The first manifestation affects the OIDC JWKS (JSON Web Key Set) and Metadata Document caches. When evaluating whether cached data remains valid, the code incorrectly uses isBefore instead of isAfter, causing the cache validation to always fail. Consequently, every incoming request triggers a fresh HTTP fetch to the OIDC provider, completely bypassing the caching mechanism and potentially overwhelming both the DSF service and the external OIDC provider with redundant requests.
The second manifestation inversely affects the OIDC token cache for FHIR client connections. The same inverted comparison causes tokens to never be marked as expired, meaning the cache continues returning stale tokens indefinitely. This creates a security risk where expired authentication tokens remain in active use, potentially allowing unauthorized access after tokens should have been invalidated.
Root Cause
The root cause is improper control flow logic within the time comparison operations of the caching subsystem. The developer mistakenly used isBefore temporal comparison where isAfter was required, inverting the intended cache behavior. This type of error represents a common coding mistake where boolean logic produces the opposite of the intended effect, fundamentally breaking cache expiration and refresh mechanisms.
Attack Vector
The vulnerability is exploitable over the network without authentication. An attacker could exploit this vulnerability in two ways:
Denial of Service via Resource Exhaustion: By sending numerous requests to a DSF instance, an attacker could trigger excessive outbound HTTP requests to the OIDC provider. Since the metadata and JWKS caches never return cached values, each request generates new HTTP fetches, potentially exhausting network resources, connection pools, or rate limits on the OIDC provider.
Authentication Bypass via Stale Tokens: The never-invalidating token cache means expired OIDC tokens continue to be used for FHIR client connections. If a token's underlying permissions have been revoked or the user's access should have expired, the system continues honoring the stale cached token, effectively bypassing intended security controls.
The vulnerability mechanism involves inverted time comparison logic in the DSF caching implementation. The JWKS and Metadata Document caches fail to return cached values because the validation incorrectly checks if the current time is before the cache timestamp rather than after, causing perpetual cache misses. Conversely, the token cache uses the same inverted logic for expiration, preventing tokens from ever being marked as expired. For complete technical details, refer to the GitHub Security Advisory.
Detection Methods for CVE-2026-40942
Indicators of Compromise
- Abnormally high volume of outbound HTTP requests to OIDC provider endpoints from DSF servers
- Log entries showing repeated JWKS and metadata document fetches for each incoming request
- OIDC tokens being used beyond their expected expiration timestamps in FHIR client connections
- Performance degradation in DSF services correlated with increased authentication traffic
Detection Strategies
- Monitor network traffic patterns for excessive connections to OIDC provider well-known endpoints
- Implement logging analysis to detect cache miss ratios approaching 100% for OIDC metadata
- Audit authentication tokens in FHIR client sessions for expired validity timestamps
- Compare actual OIDC provider request volumes against expected cached request patterns
Monitoring Recommendations
- Configure alerting for outbound HTTP request rate anomalies to OIDC endpoints
- Implement token lifetime tracking to detect tokens used beyond expiration
- Establish baseline metrics for cache hit ratios and alert on significant deviations
- Monitor DSF service performance metrics for degradation indicative of cache failure
How to Mitigate CVE-2026-40942
Immediate Actions Required
- Upgrade Data Sharing Framework (DSF) to version 2.1.0 or later immediately
- Review OIDC provider logs to assess potential impact from excessive request volumes
- Audit FHIR client session logs to identify any use of expired authentication tokens
- Consider implementing rate limiting on outbound OIDC requests as a temporary safeguard
Patch Information
The vulnerability is fixed in DSF version 2.1.0. The patch corrects the inverted time comparison logic by replacing isBefore with isAfter in both cache implementations. Two specific commits address this issue:
- Commit 31c2e97 - Cache update fix
- Commit d3ca59b - Cache change fix
Additional details are available in the GitHub Security Advisory GHSA-xmj9-7625-f634.
Workarounds
- If immediate upgrade is not possible, consider implementing external caching proxies for OIDC endpoints
- Implement network-level rate limiting to protect OIDC providers from excessive requests
- Reduce token cache TTL configurations to minimize window of stale token usage
- Deploy monitoring to detect and alert on symptoms until patching is complete
# Verify DSF version after upgrade
dsf --version
# Expected output: 2.1.0 or higher
# Review configuration for cache settings
cat /etc/dsf/config.yaml | grep -A 10 "oidc:"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
