CVE-2021-27434
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedProducts with Unified Automation .NET based OPC UA Client/Server SDK Bundle: Versions V3.0.7 and prior (.NET 4.5, 4.0, and 3.5 Framework versions only) are vulnerable to an uncontrolled recursion, which may allow an attacker to trigger a stack overflow.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceUnified Automation's .NET-based OPC UA Client/Server SDK (versions 3.0.7 and prior for .NET Framework 4.5/4.0/3.5) contains an uncontrolled recursion vulnerability that can be exploited to trigger a stack overflow, causing denial of service. The vulnerability stems from missing recursion depth limits in certain SDK operations, allowing maliciously crafted OPC UA messages or sequences to cause excessive recursive calls.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data<= 3.0.7CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
-
Identify if Unified Automation OPC UA SDK is in useSearch your application dependencies, project references, or installed components for 'UnifiedAutomation.UaSdk' or related .NET assemblies from Unified Automation. Review your NuGet packages, bin directories, or GAC for these DLLs.Affected if The Unified Automation .NET-based OPC UA Client/Server SDK is present in your environment.
-
Determine the installed SDK versionInspect the version information of the Unified Automation SDK assemblies (typically found in assembly metadata or NuGet package version). Check your project's packages.config, .csproj file references, or the actual DLL properties.Affected if The SDK version is 3.0.7 or any version prior to it (3.0.0 through 3.0.7).
-
Confirm OPC UA message processing is enabledVerify that your application or service initializes and uses the OPC UA SDK to process incoming OPC UA messages. Check if your server or client application creates UaServer or UaClient instances and enables message handling loops.Affected if The SDK is actively processing OPC UA messages from network sources, which triggers the vulnerable recursive code paths.
-
Check for application-level recursion guardsInspect your application code or SDK configuration for custom recursion depth limits, input validation on OPC UA message handling, or stack overflow protection mechanisms around recursive SDK operations.Affected if No application-level recursion limits or input validation exist on OPC UA message handling paths, leaving the vulnerability fully exposed.
You are affected if the Unified Automation .NET OPC UA SDK version 3.0.7 or earlier is deployed and actively processing OPC UA network messages without additional recursion safeguards.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataUpgrade to a patched version of the SDK if available; otherwise, implement application-level recursion guards and input validation on OPC UA message handling paths, and restrict network access to OPC UA servers using the affected SDK.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,888.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-27434 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-27434 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data