STATUS_FREE_VM_NOT_AT_BASE (0XC000009F) Fix & Root Cause

This Windows error means the memory manager tried to free virtual memory at an address that isn't the base of the allocation. Usually triggered by buggy drivers or corrupted memory.

You're working away, maybe compiling code, running a VM, or just opening a heavy application, and then—boom—blue screen. The error code is 0XC000009F, and the message says STATUS_FREE_VM_NOT_AT_BASE. I've seen this one pop up most often on systems with third-party antivirus, certain VPN clients (especially Cisco AnyConnect or OpenVPN), or after a Windows update that didn't play nice with the GPU driver.

The core issue is simple: the Windows memory manager is strict about how virtual memory gets allocated and freed. When a driver or piece of software asks the kernel to free a block of memory, it has to pass back the exact base address that was given when the block was allocated. If it passes any other address—even off by one byte—the kernel throws 0XC000009F and crashes the system. That's usually a bug in the driver or a sign of physical memory corruption.

Why This Happens — A Real World Trigger

Imagine you're running a memory-intensive Python script that uses NumPy arrays, and your GPU driver (NVIDIA or AMD) tries to map some of that memory into the video card's address space. If the GPU driver's memory management code has a bug that calculates the wrong base address when freeing the mapping, you'll hit this error. I've also seen it with outdated virtualization software like VMware Workstation version 15 or older—their memory allocators had a known issue with Windows 10 2004 and later.

Fix 1: Run Driver Verifier (the real fix)

Driver Verifier is the nuclear option, but it's the only way to pinpoint which driver is at fault. Don't skip this if you want a permanent fix.

Open Command Prompt as Administrator.
Type verifier and hit Enter.
Select "Create custom settings" and click Next.
Check all boxes except "DDI compliance checking" (it's noisy).
Select "Select driver names from a list".
Click "Add Unpublished Drivers" at the bottom.
Sort by provider—look for third-party drivers: NVIDIA, AMD, Realtek, Intel, your VPN, antivirus, or any hardware vendor. Do NOT add Microsoft drivers.
Click Finish, then restart your PC.

Your system will boot, and then crash again—but this time it'll generate a memory dump that points directly to the guilty driver. Use WinDbg or just note the filename from the blue screen. Once you identify it, update or uninstall that driver.

Fix 2: Check for Memory Corruption

If Driver Verifier doesn't catch anything, it's likely bad RAM. Run Windows Memory Diagnostic:

Press Win + R, type mdsched.exe, hit Enter.
Choose "Restart now and check".
Let it run the standard test (takes about 20-30 minutes).

If it finds errors, replace the faulty stick. If it passes, run MemTest86 for a thorough test (allow 4+ hours). I've seen memory corruption that passes Windows' quick test but fails MemTest86 after a few passes.

Fix 3: Clean Boot to Isolate Software

Sometimes a driver isn't the problem—a poorly written service is. Try a clean boot:

Press Win + R, type msconfig.
Under Services tab, check "Hide all Microsoft services", then click "Disable all".
Under Startup tab, open Task Manager and disable all startup items.
Restart. If the error stops, re-enable services one by one until you find the culprit.

What if it still fails?

Update BIOS/firmware: Manufacturers sometimes fix memory management bugs in BIOS updates. Check your motherboard vendor's site.
Disable hardware virtualization: In BIOS, turn off Intel VT-x or AMD-V. This might help if the error happens in VMs.
Roll back Windows Update: If the error started after a recent update, go to Settings → Update & Security → View update history → Uninstall updates. Remove the latest one.
Run SFC and DISM: Open Command Prompt as Admin and run sfc /scannow, then DISM /Online /Cleanup-Image /RestoreHealth. This fixes system file corruption that could trigger this error.

I know how annoying this error is—it's cryptic and feels random. But stick with Driver Verifier first. Nine times out of ten, it'll reveal a driver you thought was fine but was actually doing something dumb with memory. Good luck, and let me know which fix worked for you.