the flood that looks like a failure
Almost everyone who deploys WDAC in audit mode for the first time has the same experience. The policy goes live, the Code Integrity operational log starts filling up, and a large share of the events point at files ending in ni.dll.
The instinct is reasonable. The events are real, the volume is high, and the natural next step is to start authoring rules to make them stop. So people capture hashes, build allow rules, and watch the log keep producing more of the same files with different hashes after the next servicing update.
This is one of the most common early stumbles in an application control program, and it is worth understanding once, properly, because the answer saves a great deal of wasted effort. I lost more time to this than I am comfortable admitting when I started.
what a ni.dll file actually is
The ni in ni.dll stands for native image. These files are the precompiled native output of the .NET runtime, produced by NGen or by the runtime itself, from managed assemblies that are already present on the machine.
A managed .NET assembly ships as MSIL, which is an intermediate form that has to be compiled to native code before it runs. To avoid paying that compilation cost every time, the runtime can generate a native image ahead of execution and cache it. Those cached native images are the ni.dll files. They live in locations like the native image cache under the .NET framework directories and the NativeImages folders.
The key fact is that they are derived artifacts. A ni.dll is not a piece of software that arrived on the machine. It is a machine-specific, version-specific byproduct of an assembly you already have, generated on the fly to make that assembly start faster.
why they do not belong in your policy
Once you understand what they are, the reason they should not be added to a policy follows directly.
- they are derived from managed assemblies that your policy already covers — the original DLL or EXE is the thing that matters, and a publisher or hash rule on it is the correct control point
- their hashes are volatile — a native image is specific to the machine, the runtime version, and the exact assembly it was compiled from, so the hash you capture today is invalidated by the next .NET servicing update
- authoring rules for them produces brittle policy — every hash rule you add for a native image is a rule that will silently stop matching after an update, leaving you with policy bloat and no lasting benefit
- the runtime regenerates them freely — chasing them with rules is chasing a moving target that the operating system recreates whenever it sees fit
In short, you would be writing rules for a byproduct rather than for the software. The software is already handled. The byproduct is noise.
how to triage them correctly
The practical workflow when you are working through audit events is straightforward.
- identify the flagged file — if it ends in ni.dll, treat it as a candidate for suppression rather than a candidate for a rule
- confirm the path — legitimate native images sit in the .NET native image cache locations, so verify the file is actually in one of those directories
- confirm the parent assembly is allowed — the managed assembly the native image was compiled from is the thing your policy should cover, so make sure it is
- then ignore the native image event itself — do not mint a hash rule for it
That third and fourth step together are the whole answer. The event is telling you the runtime generated a native image. It is not telling you that anything needs a rule.
the caveat that keeps audit mode useful
There is one discipline worth keeping, and it is the reason audit mode exists in the first place.
Do not suppress on the ni.dll extension alone. A file named to look like a native image, but sitting in a directory where native images have no business being, is exactly the kind of thing audit mode is there to surface. The combination that makes a native image safe to ignore is the extension and a legitimate cache path together, not the extension by itself.
This is a small point, but it is the difference between filtering noise and building a blind spot. The whole value of running in audit mode before you enforce is that it shows you everything. The goal is to learn to recognise the noise quickly, not to teach yourself to stop looking.
the takeaway
The native image events are not a problem to solve. They are a category of event to recognise.
When you see ni.dll files generating Code Integrity events early in a rollout, the correct response is to confirm the parent assembly is covered, confirm the file sits in a real native image cache path, and move on. No rule. No hash. No policy entry.
Learning to separate signal from noise in the audit log is most of what makes the early phase of a WDAC program manageable. The native image events are the first and most common piece of noise nearly everyone meets. Recognising them for what they are is a small thing that removes a surprising amount of wasted effort.
This kind of triage logic — knowing which events deserve a rule and which are byproducts to ignore — is exactly the sort of operational knowledge WDACManager is built to encode, so that the person working through an audit log is not relearning it from scratch every time.