EUVD-2026-53680
GHSA-2cg2-hxr7-q7f4
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Network-reachable OPC UA server, no credentials needed for anonymous sessions, pure availability impact with no confidentiality or integrity loss.
Primary rating from Vendor (mitre).
CVSS VectorVendor: mitre
Lifecycle Timeline
4DescriptionCVE.org
An issue in Systerel S2OPC 1.7.3 allows a remote attacker to cause a denial of service via the event monitored-item queue resize handling
AnalysisAI
Denial of service in Systerel S2OPC 1.7.3 allows remote unauthenticated attackers to crash or render unavailable an OPC UA server by sending crafted requests that trigger uncontrolled resource consumption in the event monitored-item queue resize handling. Affected source code is confirmed across subscription_core.c and monitored_item_notification_queue_bs.c. No public exploit code has been identified at time of analysis, and this vulnerability is not listed in the CISA KEV catalog.
Technical ContextAI
S2OPC is an open-source OPC UA (Open Platform Communications Unified Architecture) stack developed by Systerel, designed for safety and security-critical industrial environments including ICS and SCADA systems. OPC UA subscriptions allow clients to monitor server-side data changes via monitored items; a ModifyMonitoredItems service call can request a change to the queue size for event-based monitored items. CWE-400 (Uncontrolled Resource Consumption) indicates the flaw lies in insufficient bounds-checking or rate-limiting during these queue resize operations, allowing an attacker to exhaust server-side memory or processing capacity. The affected code paths are confirmed in src/ClientServer/services/b2c/monitored_item_notification_queue_bs.c and src/ClientServer/services/bgenc/subscription_core.c within the 1.7.3 release tag.
RemediationAI
The primary remediation is to monitor the Systerel S2OPC GitLab repository and apply any patch released in a version beyond 1.7.3; no specific fixed version is confirmed in the available data - the GitLab work item 1788 should be tracked for patch release status. As a compensating control, operators should restrict OPC UA server port access (typically TCP 4840) to trusted client IP ranges using network-layer ACLs or firewalls, reducing the unauthenticated attack surface - note this does not eliminate the flaw but significantly raises attacker cost. Additionally, enabling OPC UA security policies that require authenticated sessions (disabling Anonymous security mode) would require PR:L/PR:H, eliminating unauthenticated exploitation paths, at the cost of additional client credential management overhead. Operators in safety-critical environments should assess whether temporary disabling of event-based monitored item subscription support (if configurable) is feasible as a hardening measure until a patch is available.
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Same weakness CWE-400 – Uncontrolled Resource Consumption
View allSame technique Denial Of Service
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External POC / Exploit Code
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