CVE-2026-18785 Overview
CVE-2026-18785 is a use-after-free vulnerability in the open62541 open-source OPC UA (Open Platform Communications Unified Architecture) implementation. The flaw exists in the UA_Client_getRemoteDataTypes function within examples/custom_datatype/client_types_custom.c. An attacker with local access and low privileges can manipulate the affected code path to trigger memory corruption. The vulnerability was reported against commit ca356b088ada7dee824d1b4acd07c1ff07ce242b. The project closed the associated issue, noting that the report did not follow the official security disclosure process. A public disclosure exists, but no vendor patch is currently referenced.
Critical Impact
Local exploitation of the use-after-free condition [CWE-119] in UA_Client_getRemoteDataTypes can lead to memory corruption affecting confidentiality, integrity, and availability of the client process.
Affected Products
- open62541 OPC UA implementation (commit ca356b088ada7dee824d1b4acd07c1ff07ce242b)
- Example client component examples/custom_datatype/client_types_custom.c
- Applications embedding the affected UA_Client_getRemoteDataTypes example code
Discovery Timeline
- 2026-08-04 - CVE-2026-18785 published to NVD
- 2026-08-04 - Last updated in NVD database
Technical Details for CVE-2026-18785
Vulnerability Analysis
The vulnerability is a use-after-free condition in the UA_Client_getRemoteDataTypes function of the open62541 project. This function is part of the custom data type example client code shipped in examples/custom_datatype/client_types_custom.c. Use-after-free flaws occur when a program continues to reference memory after it has been released, allowing an attacker to influence the contents of the freed region and manipulate program behavior.
The classification maps to [CWE-119], which describes improper restriction of operations within the bounds of a memory buffer. Exploitation requires local access to the host running the vulnerable client and low privileges. Successful triggering of the flaw can corrupt heap metadata, cause the process to crash, or allow controlled overwrites of dangling pointers.
The upstream project closed the GitHub issue tracking this report, stating that the submission did not follow the official security disclosure process for open62541. No vendor patch has been referenced against the affected commit at the time of publication.
Root Cause
The root cause is improper lifetime management of a heap-allocated object referenced by UA_Client_getRemoteDataTypes. The example code releases the underlying memory while a pointer to that memory remains in use, producing a dangling reference. Subsequent access to the dangling pointer results in the use-after-free condition.
Attack Vector
The attack vector is local. An adversary with the ability to influence inputs consumed by an application built on the affected example code can trigger the vulnerable code path. Because the exploit has been publicly disclosed, defenders should assume that proof-of-concept material is accessible. See the GitHub Issue Discussion and the VulDB Vulnerability Report for additional technical context.
No verified exploit code is reproduced here. Refer to the referenced advisories for further detail on the triggering sequence.
Detection Methods for CVE-2026-18785
Indicators of Compromise
- Unexpected termination or segmentation faults in processes linking the open62541 custom data type client example.
- Heap corruption diagnostics emitted by AddressSanitizer or Valgrind referencing UA_Client_getRemoteDataTypes or client_types_custom.c.
- Local user activity invoking OPC UA client binaries built from the affected commit ca356b088ada7dee824d1b4acd07c1ff07ce242b.
Detection Strategies
- Perform source-level review of any deployed code derived from examples/custom_datatype/client_types_custom.c for use-after-free patterns.
- Rebuild affected client binaries with AddressSanitizer to surface dangling pointer access during runtime testing.
- Monitor for crash telemetry from OPC UA client processes and correlate against local user sessions.
Monitoring Recommendations
- Track process crash events on hosts running OPC UA clients and forward them to centralized logging.
- Baseline expected behavior of OPC UA client processes and alert on anomalous child process creation or memory faults.
- Review file integrity monitoring on OPC UA client binaries and their dependencies.
How to Mitigate CVE-2026-18785
Immediate Actions Required
- Identify any production or embedded software derived from the open62541 custom_datatype example and inventory affected builds.
- Restrict local access to hosts running the vulnerable client until a fix is applied.
- Treat the affected example code as reference material only and avoid shipping it directly in production images.
Patch Information
No vendor patch has been published against commit ca356b088ada7dee824d1b4acd07c1ff07ce242b at the time of writing. The upstream project closed the reporting issue because the disclosure did not follow the official security process. Downstream maintainers should track the open62541 issue tracker and the VulDB CVE Report for updates.
Workarounds
- Remove or refactor calls to UA_Client_getRemoteDataTypes from production builds derived from the example code.
- Apply local access controls to limit which users can invoke the affected client binaries.
- Rebuild affected components with compiler hardening flags such as -fsanitize=address during testing and hardened allocator options in production.
# Configuration example
# Rebuild affected client with AddressSanitizer to surface use-after-free at runtime
CFLAGS="-O1 -g -fsanitize=address -fno-omit-frame-pointer" \
LDFLAGS="-fsanitize=address" \
cmake -DUA_BUILD_EXAMPLES=OFF -DCMAKE_BUILD_TYPE=Debug ..
make -j"$(nproc)"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
