# CVE-2026-67856: open62541 denial of service via subscription requests

Source: https://junglewise.ai/threats/cve-2026-67856-open62541-denial-of-service-via-subscription-requests  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-04. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-67856 · Severity: high · CVSS 7.5 · Published 2026-08-04

open62541 is an open-source OPC UA server library used in industrial control systems and IoT applications. A remote attacker can crash OPC UA servers using specially crafted subscription management requests (CreateSubscription, CreateMonitoredItems, Publish, TransferSubscriptions, DeleteSubscriptions), causing service downtime without requiring authentication. This impacts operational technology environments relying on OPC UA for real-time data exchange.

## Quick answers

**Is CVE-2026-67856 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-67856 being exploited in the wild.

**How severe is CVE-2026-67856?** High severity, with a CVSS score of 7.5, published 4 August 2026.

**Which products and versions are affected?** open62541 open62541 1.5.5 and before.

**Is there a fix for CVE-2026-67856?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-67856 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-67856?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a denial of service flaw in open62541's subscription service handler (ua_services_subscription.c). A remote attacker can trigger a crash or resource exhaustion by sending malformed OPC UA service requests related to subscription lifecycle management, including CreateSubscription, CreateMonitoredItems with sampling, Publish, TransferSubscriptions, and DeleteSubscriptions operations. The vulnerability requires network reachability to the OPC UA server but does not require authentication. No patch version information has been confirmed in the advisory, though versions 1.5.5 and earlier are affected.

## Affected products

- open62541 open62541 1.5.5 and before

## Timeline

- 2026-08-04: disclosed

## References

- [https://github.com/open62541/open62541/blob/master/examples/access_control/server_access_control.c](https://github.com/open62541/open62541/blob/master/examples/access_control/server_access_control.c)
- [https://github.com/open62541/open62541/blob/master/src/server/ua_services_subscription.c](https://github.com/open62541/open62541/blob/master/src/server/ua_services_subscription.c)