CVE-2026-67869 Overview
CVE-2026-67869 is a buffer overflow vulnerability in open62541 v1.5.5, an open-source implementation of the OPC Unified Architecture (OPC UA) protocol. The flaw resides in the Service_Call handler, which validates client-supplied input arguments against runtime-resolved InputArguments metadata. A remote unauthenticated attacker can exploit this weakness to trigger a denial of service against affected OPC UA servers. The vulnerability affects industrial automation and Internet of Things (IoT) deployments that rely on open62541 for machine-to-machine communication.
Critical Impact
Remote unauthenticated attackers can crash open62541 v1.5.5 OPC UA servers over the network, disrupting industrial control processes and dependent operational technology (OT) workflows.
Affected Products
- open62541 v1.5.5
- OPC UA servers built with the affected open62541 library version
- Industrial and IoT applications embedding open62541 v1.5.5
Discovery Timeline
- 2026-08-06 - CVE-2026-67869 published to NVD
- 2026-08-06 - Last updated in NVD database
Technical Details for CVE-2026-67869
Vulnerability Analysis
The vulnerability affects the OPC UA Call service implementation in open62541. When a client invokes a method, the server validates the supplied input arguments against InputArguments metadata that is resolved at runtime. Inadequate boundary enforcement during this validation leads to a buffer overflow condition. Attackers can send crafted Call service requests over the network to trigger the overflow and crash the server process. The impact is limited to availability, with no confidentiality or integrity compromise reported.
Root Cause
The root cause is improper validation of input argument sizes against the runtime-resolved InputArguments metadata inside Service_Call. When argument data exceeds the assumed bounds, memory adjacent to the destination buffer is corrupted. The implementation trusts the structural conformance of the incoming arguments without enforcing a strict length check tied to the resolved method definition.
Attack Vector
Exploitation occurs remotely over the network without authentication or user interaction. An attacker connects to an exposed OPC UA endpoint and issues a malformed Call request whose input arguments deviate from the expected metadata. The overflow terminates the server, denying service to legitimate OPC UA clients. Refer to the GitHub Method Service Implementation and GitHub Issue #8171 Discussion for source-level context.
No verified public exploit code is available. See the referenced GitHub Subscription Conditions Implementation and GitHub Example Alarm Server for related code paths.
Detection Methods for CVE-2026-67869
Indicators of Compromise
- Unexpected termination or repeated restarts of open62541-based OPC UA server processes.
- OPC UA Call service requests with input argument counts or sizes that do not match the target method's declared InputArguments.
- Network connections to OPC UA TCP port 4840 from untrusted or unexpected sources immediately preceding a server crash.
Detection Strategies
- Inspect OPC UA traffic for malformed Call requests where argument payload length diverges from the server-published method signature.
- Correlate process crash events on OPC UA hosts with concurrent inbound sessions to the OPC UA endpoint.
- Track open62541 version fingerprints exposed during OPC UA session establishment to identify vulnerable v1.5.5 instances.
Monitoring Recommendations
- Log and alert on abnormal restart cycles of OPC UA server services and supervisord or systemd unit failures.
- Baseline expected OPC UA client identities and flag deviations, particularly from external network segments.
- Forward OPC UA server logs and host telemetry to a centralized analytics platform for cross-correlation with network detections.
How to Mitigate CVE-2026-67869
Immediate Actions Required
- Inventory all systems running open62541 v1.5.5 and prioritize those exposing OPC UA endpoints to untrusted networks.
- Restrict access to OPC UA TCP port 4840 using firewall rules or OT network segmentation until a fixed version is deployed.
- Require certificate-based authentication and encrypted OPC UA security policies to limit exposure to unauthenticated callers.
- Monitor the upstream open62541 project for a patched release addressing Service_Call argument validation.
Patch Information
No vendor patch reference is listed in the NVD entry at publication. Track the GitHub Issue #8171 Discussion and the open62541 repository for a maintainer fix and updated release beyond v1.5.5.
Workarounds
- Place vulnerable OPC UA servers behind an application-aware gateway that validates Call request arguments against method metadata before forwarding.
- Disable exposure of method-based nodes that are not required for production workflows to reduce the attack surface of Service_Call.
- Enforce network allow-lists so only known OPC UA clients can reach the server endpoint.
# Example: restrict OPC UA endpoint to trusted OT subnet with iptables
iptables -A INPUT -p tcp --dport 4840 -s 10.20.30.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 4840 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
