CVE-2026-90782 in S2OPC
Summary
by MITRE • 09/13/2026
S2OPC through 1.7.3 contains a null pointer dereference in msg_subscription_publish_bs__alloc_notification_message_items() where a failed allocation for DataChangeNotification is overwritten by a successful allocation for EventNotificationList. Attackers can trigger heap allocation failures on sessions with both data-change and event notifications to cause the server process to terminate.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/13/2026
The vulnerability identified in S2OPC versions through 1.7.3 represents a critical memory management flaw located within the msg_subscription_publish_bs__alloc_notification_message_items function. This specific component is responsible for handling the allocation of notification items required for publishing subscription updates, which are fundamental to the OPC UA protocol's ability to deliver real-time data and event notifications to clients. The core technical issue stems from an improper error handling sequence during dynamic memory allocation operations. When the system attempts to allocate memory for a DataChangeNotification structure, it may encounter a failure due to resource exhaustion or other constraints. In a robust implementation, this failure should trigger immediate cleanup of any previously allocated resources and return an appropriate error code without proceeding further. However, in the affected versions, the logic fails to properly manage state when the initial allocation attempt for DataChangeNotification fails.
Instead of aborting the operation or handling the partial state correctly, the execution flow continues to a subsequent step where it attempts to allocate memory for EventNotificationList. If this second allocation succeeds, the code overwrites pointers or internal structures that were intended to track the failed DataChangeNotification allocation. This overwrite effectively masks the initial failure and leaves the system in an inconsistent state regarding its heap management metadata. The critical consequence of this logic error is a null pointer dereference when the application later attempts to access or process the notification data associated with the session. Because the original allocation for DataChangeNotification was not properly cleaned up or marked as invalid, subsequent operations assume valid memory addresses that no longer exist or point to corrupted regions, leading directly to an unhandled exception and the termination of the server process.
From a security impact perspective, this vulnerability facilitates Denial of Service attacks against OPC UA servers running S2OPC libraries. An attacker who can interact with sessions configured to subscribe to both data-change events and event notifications can trigger heap allocation failures by manipulating network traffic or exhausting system resources in specific ways. By forcing the server into the flawed code path where a DataChangeNotification allocation fails but an EventNotificationList allocation succeeds, the attacker induces the null pointer dereference that crashes the service. This results in immediate availability loss for all clients connected to the affected OPC UA server. In industrial control systems or critical infrastructure environments relying on OPC UA for monitoring and control, such unexpected terminations can lead to significant operational disruptions, potential safety hazards if fail-safe mechanisms are not robustly implemented, and increased maintenance overhead due to frequent service restarts.
The technical classification of this flaw aligns with CWE-476, which denotes a NULL Pointer Dereference vulnerability resulting from improper handling of error conditions during memory allocation. Furthermore, the exploitation technique relates to ATT&CK tactic T1499, Endpoint Denial of Service, specifically under techniques that involve resource exhaustion or application crashes via malformed input sequences. The root cause is categorized under CWE-755, Improper Handling of Exceptional Conditions, as the software fails to correctly handle a runtime error condition (allocation failure) and proceeds with invalid state assumptions. This highlights a broader issue in embedded C programming where manual memory management requires rigorous validation at every step, particularly when multiple allocations are performed within a single logical operation block.
Mitigation strategies for this vulnerability primarily involve upgrading the S2OPC library to version 1.7.4 or later, where the allocation logic has been corrected to ensure that failures in one part of the notification structure do not corrupt the state required by subsequent parts. For organizations unable to immediately patch their systems, defensive coding practices should be reviewed within custom integrations using this library. Developers must implement strict checks after every dynamic memory allocation call, ensuring that if any single allocation fails, all previously allocated resources are freed and the function returns an error code without proceeding further. Additionally, implementing heap sanitizers during development and testing phases can help detect such null pointer dereferences before deployment. Network-level monitoring should also be employed to identify anomalous patterns of subscription requests or resource consumption that might indicate attempts to exploit this specific allocation failure scenario, allowing for proactive blocking of malicious traffic targeting vulnerable OPC UA endpoints.