# CVE-2026-18257: Systerel S2OPC Improper Certificate Validation in CycloneCrypto

Source: https://junglewise.ai/threats/cve-2026-18257-systerel-s2opc-improper-certificate-validation-in-cyclonecrypto  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-29. Updated: 2026-07-29  
License: CC BY 4.0 with a link back

CVE-2026-18257 · Severity: medium · CVSS 5.6 · Published 2026-07-29

A security flaw exists in S2OPC, an open-source implementation of the OPC UA communication protocol used in industrial automation. The software fails to properly check if a master security certificate has expired, which could allow unauthorized or outdated systems to be incorrectly trusted. This could potentially lead to unauthorized access or data manipulation within industrial control environments.

Technologies: [Systerel S2OPC](https://junglewise.ai/threats/technologies/s2opc). Vendors: [Systerel](https://junglewise.ai/threats/vendors/systerel).

## Quick answers

**Is CVE-2026-18257 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-18257 being exploited in the wild.

**How severe is CVE-2026-18257?** Medium severity, with a CVSS score of 5.6, published 29 July 2026.

**Which products and versions are affected?** Systerel S2OPC >= 1.5.0, < 2.0.0.

**Is there a fix for CVE-2026-18257?** 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-2026-18257 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-18257?** Check whether you run Systerel S2OPC at an affected version. 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

An improper certificate validation vulnerability (CWE-295) exists in the CycloneCrypto cryptographic wrapper of S2OPC. The root cause is a failure to correctly verify the validity period of a root issuer certificate during the chain of trust validation. A remote attacker could potentially present a certificate signed by an expired or otherwise invalid root CA, which the system would incorrectly accept as trusted. This affects S2OPC versions 1.5.0 through 1.9.x and is addressed in version 2.0.0. Exploitation requires a high-complexity environment where the attacker can intercept or initiate network communication.

## Affected products

- Systerel S2OPC >= 1.5.0, < 2.0.0

## Timeline

- 2026-07-29: disclosed
- 2026-07-29: advisory

## References

- [https://gitlab.com/systerel/S2OPC/-/work_items/1804](https://gitlab.com/systerel/S2OPC/-/work_items/1804)

## Related threats

- [S2OPC null pointer dereference in notification message allocation](https://junglewise.ai/threats/cve-2026-90782-s2opc-null-pointer-dereference-in-notification-message-allocation)
- [Systerel S2OPC use-after-free in monitored item event filter](https://junglewise.ai/threats/cve-2026-82619-systerel-s2opc-use-after-free-in-monitored-item-event-filter)
- [Systerel S2OPC out-of-bounds read in string array range writing](https://junglewise.ai/threats/cve-2026-82618-systerel-s2opc-out-of-bounds-read-in-string-array-range-writing)
- [Systerel S2OPC out-of-bounds read in AddNodes Service](https://junglewise.ai/threats/cve-2026-78049-systerel-s2opc-out-of-bounds-read-in-addnodes-service)
- [Systerel S2OPC heap-based buffer overflow in EventFilter handling](https://junglewise.ai/threats/cve-2026-67868-systerel-s2opc-heap-based-buffer-overflow-in-eventfilter-handling)