# CVE-2026-6899: Improper Check for Certificate Revocation in S2OPC

> Attackers can bypass certificate revocation checks in S2OPC by exploiting CRL handling flaws, allowing connections with revoked certificates.

- **Severity:** Medium 5.6 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Jun 2026
- **Updated:** 9 Jun 2026
- **Also known as:** GHSA-j893-vcpr-rgfc

## What is CVE-2026-6899?

CVE-2026-6899 is a medium-severity vulnerability in Systerel S2OPC, published on 9 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Check for certificate revocation only considers the first matching CRL and ignores other valid CRLs of the same CA in the CycloneCrypto cryptographic wrapper of S2OPC library. It might allow connection between an OPC UA client and server using a revoked certificate.

Weakness: CWE-299 (Improper Check for Certificate Revocation)

## Which versions are affected by CVE-2026-6899?


## How do I fix CVE-2026-6899?

No fix has been published for CVE-2026-6899 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-6899 being exploited?

There is no known exploitation of CVE-2026-6899 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6899 and fix it if it is affected.

What it is: CVE-2026-6899 is a medium-severity vulnerability in Systerel S2OPC, published on 9 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-6899 in the wild and no public exploit code.

Affected product: Systerel S2OPC. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-6899/ (Markdown: https://insights.sbomify.com/CVE-2026-6899/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6899
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6899
- OSV: https://osv.dev/vulnerability/CVE-2026-6899

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6899/
Summaries are generated and may contain mistakes; the official description above is the record.