# CVE-2026-18784: open62541 heap buffer overflow in UA_Client_readNodeClassAttribute

Source: https://junglewise.ai/threats/cve-2026-18784-open62541-heap-buffer-overflow-in-ua-client  
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-2026-18784 · Severity: medium · CVSS 5.3 · Published 2026-08-04

open62541 is an open-source OPC UA library used in industrial control systems, gateways, and diagnostic tools to communicate with servers. A malicious OPC UA server can trigger a heap-based buffer over-read in the client library when reading node class attributes, causing the client process to crash and resulting in denial of service of critical industrial infrastructure components.

## Quick answers

**Is CVE-2026-18784 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-18784 being exploited in the wild.

**How severe is CVE-2026-18784?** Medium severity, with a CVSS score of 5.3, published 4 August 2026.

**Which products and versions are affected?** open62541 open62541 up to 1.5.5.

**Is there a fix for CVE-2026-18784?** 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-2026-18784 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-18784?** 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

A heap buffer over-read exists in the __Client_readAttribute() function in src/client/ua_client_highlevel.c. The vulnerable code path for UA_ATTRIBUTEID_NODECLASS skips type validation and unconditionally reads sizeof(UA_NodeClass) bytes (4 bytes) from a variant field without confirming the variant actually contains a NodeClass type. If a malicious server responds with a Boolean (1 byte) instead, a 4-byte out-of-bounds read occurs. The attack is reachable via a real OPC UA TCP handshake (HEL/ACK → OpenSecureChannel → FindServers → GetEndpoints → Read). The primary impact is remote denial of service; industrial clients connecting to untrusted or compromised servers are at risk. Patches are expected from the open62541 project.

## Affected products

- open62541 open62541 up to 1.5.5

## Timeline

- 2026-08-04: disclosed: Published on NVD
- 2026: other: Exploit made public; project report closed, stating not official reporting channel

## References

- [https://github.com/gff-cw/information/issues/11](https://github.com/gff-cw/information/issues/11)
- [https://github.com/open62541/open62541/issues/8139](https://github.com/open62541/open62541/issues/8139)