How to fix ucrtbase.dll application error on Windows?

A ucrtbase.dll application error means a program crashed while it was running code of the Universal C Runtime, a part of Windows. The DLL is usually the place of the crash, not its cause. Read the crash record first, then update or repair the program that crashed.

Facts checked on 15 October 2026. Steps written for Windows 11 (25H2 and 26H2) and Windows 10 22H2.

What the ucrtbase.dll application error means

ucrtbase.dll is the Universal C Runtime, or UCRT. It holds the basic functions of the C language that almost every program for Windows uses: memory, text, files, maths. Microsoft states that the UCRT is an operating system component, included as part of Windows 10 or later and Windows Server 2016 or later.

Because so many programs use these functions, a crash of almost any program can happen while ucrtbase.dll is running. Windows then writes this DLL as the faulting module. That tells you where the crash happened, not who caused it. A program that passes broken data to a runtime function crashes inside the runtime.

Event Viewer, Windows Logs > Application, source Application Error (example record)

Faulting application name: Game.exe, version: 1.2.0.0
Faulting module name: ucrtbase.dll, version: 10.0.xxxxx.xxxx
Exception code: 0xc0000409
Faulting application path: C:\Games\Game\Game.exe
Faulting module path: C:\Windows\System32\ucrtbase.dll

Faulting application name

The program that crashed. This is the program to update or repair.

Faulting module name

ucrtbase.dll, the place of the crash. Its version starts with 10.0 and follows your Windows build.

Exception code 0xc0000409

Microsoft's __fastfail reference: the code tells Windows Error Reporting that the process is corrupted and should be ended at once. No error handler in the program runs.

Faulting module path

Should be C:\Windows\System32 or C:\Windows\SysWOW64. Any other folder is worth a look (see the download section).

• ucrtbase.dll crash or crashing: the record above. A single program or game closes. Start with Fix 1 and Fix 2.
• ucrtbase.dll not found: a program cannot start because Windows did not load the file. On Windows 10 and 11 that points to damaged system files or a very old program. Fix 3 and Fix 4.
• ucrtbased.dll was not found: a different file, the debug version of the runtime. Fix 6.

What causes ucrtbase.dll crashes, from most to least common

Most often the crashing program itself has a bug, a damaged file, a broken mod or a bad setting, and it stops inside the runtime. Less often Windows is out of date or its own system files are damaged, and then several programs fail. Rarely the cause is a debug build of a program, a recent change to the PC, or failing hardware.

ucrtbase.dll download: why a new copy does not help

Searching for a download of the file leads to DLL sites. On Windows 10 and Windows 11 such a file does nothing useful, and Microsoft's deployment documentation says why. The Universal CRT in the system directory is always used, even if a program brings a newer copy of its own, because it is a core operating system component.

• It is never loaded. A ucrtbase.dll placed next to a program's .exe file is ignored on Windows 10 and 11. The crash stays the same.
• It cannot replace the system copy safely. The copies in System32 and SysWOW64 belong to Windows and are updated by Windows Update. Overwriting them by hand breaks that.
• Its origin is unknown. A DLL from a download site can be modified. You cannot see who built it from the name.
• The real fixes are free. Windows Update brings the current runtime, and SFC and DISM restore a damaged one.

Microsoft offers separate copies of the runtime only for older Windows versions: as Windows updates, and for developers inside the Windows SDK. For an ordinary user on Windows 10 or 11 there is no separate download, because Windows already contains it.

How to fix the ucrtbase.dll application error

Fix 1 shows which program crashed, and Fix 2 repairs it, which solves the error for most readers. Fixes 3 and 4 repair Windows when many programs crash. Fix 5 covers the Visual C++ libraries, Fix 6 the debug file ucrtbased.dll, and Fix 7 a recent change.

Fix 1. Read the crash record in Event Viewer or Reliability Monitor

5 minutesNo riskYou saw ucrtbase.dll named somewhere, or a program closes without a message and you want to know why.

The record names the faulting application, its version and the exception code. Those three facts tell you which program to repair and whether Windows itself is involved, so you do not repair the wrong thing.

1. Press Win + X and select Event Viewer.
2. In the left pane, open Windows Logs and select Application.
3. In the right pane, select Filter Current Log, type 1000 in the event ID box and select OK.
4. Select the newest Application Error entry at the time of the crash.
5. On the General tab, read Faulting application name, Faulting module name and Exception code. Write them down.
6. Look through older entries. Note whether the same program appears every time, or many different ones.

1. For a simpler view, press Win + R, type perfmon /rel and press Enter to open Reliability Monitor.
2. Select a day with a red mark and double-click the Stopped working entry for the program.
3. Read the same fields under Problem signature. Fault Module Name should say ucrtbase.dll.

Fix 2. Update, repair or reinstall the program that crashes

10 to 20 minutesLow riskThe record names the same program or game as the faulting application every time.

A crash inside ucrtbase.dll with code 0xc0000409 means the program detected corrupted state and ended itself. The fault is in its code, files or data, so a vendor patch or a clean copy of its files is what removes it.

1. Check the program's site, launcher or patch notes for a newer version and install it. Vendors fix crashes of this kind in updates.
2. If you use mods, plug-ins or add-ons, start the program once without them.
3. Repair the program's files by the route in the table below.
4. If repair does not help, back up its settings or saves, then uninstall it, restart and install the current version.
5. Start the program and use it the way that used to crash.

If the crash keeps coming back with the newest version, report it to the program's maker. Give them the full Event Viewer record from Fix 1. The faulting application version and the exception code are what their developers need.

Fix 3. Install all Windows updates to update the runtime

15 to 30 minutesNo riskSeveral programs crash, Windows Update shows pending updates, or a program was updated recently and now crashes.

Microsoft states that on Windows 10 and 11 the Universal CRT version matches the version of the operating system, and that the only way to update it further is to update Windows. A program built against a newer runtime needs an up-to-date Windows.

1. Windows 11: open Settings > Windows Update. Windows 10: open Settings > Update & Security > Windows Update.
2. Select Check for updates.
3. Install everything offered, including cumulative updates.
4. Restart the PC, even if Windows does not ask for it.
5. Check for updates again until none are left, then test the program.

If an update fails to install, that is a separate problem to solve first. Step by step: Reset Windows Update components

Fix 4. Repair Windows system files with SFC and DISM

20 minutesNo riskSeveral unrelated programs crash with ucrtbase.dll, or a program reports that ucrtbase.dll is missing or not found.

On Windows 10 and 11 ucrtbase.dll is an operating system file, so the system file checker covers it. DISM first repairs the store that SFC copies good files from, then SFC replaces a damaged runtime in System32 and SysWOW64.

1. Open an elevated command window. Right-click Start and select Terminal (Admin), or type cmd in the search box, right-click Command Prompt and select Run as administrator. Select Yes when Windows asks for permission.

   

2. Run DISM first. Type the command below and press Enter. DISM downloads clean copies of damaged components from Windows Update, so it can take several minutes. Wait until it says The operation completed successfully.

   DISM.exe /Online /Cleanup-Image /RestoreHealth

   

3. Run System File Checker. In the same window, type the command below and press Enter. Do not close the window until the verification reaches 100%.

   sfc /scannow

   

4. Read the result and restart. Compare the last message with the table below this guide, then restart the PC so that repaired files are loaded.

   

These steps were written for Windows 11 24H2 and 25H2. The full page with the other versions and what each result means: Run DISM and SFC to repair Windows system files

1. When the scan ends, read its last line. "Windows Resource Protection did not find any integrity violations" means the system copy is fine.
2. If it found and repaired files, restart the PC and test the program.
3. If it could not repair some files, run the DISM command from the procedure again, restart and run SFC once more.

Fix 5. Repair the Microsoft Visual C++ Redistributable

5 minutesNo riskThe crash report or another error box also names vcruntime140.dll, vcruntime140_1.dll or msvcp140.dll.

Programs built with Visual Studio 2015 or later use ucrtbase.dll together with the Visual C++ libraries. Microsoft calls the Universal CRT a fundamental dependency of those libraries, so a damaged Visual C++ package can make a crash surface inside the runtime.

1. Open Programs and Features. Type control panel in the search box on the taskbar and select Control Panel. Select Programs > Programs and Features.
2. Find the installed versions. Look for the entries that start with Microsoft Visual C++. Each one shows a year and an architecture, x64 or x86. Several entries side by side are normal: older versions stay installed next to newer ones.

   

3. Repair each Visual C++ entry. Right-click an entry and select Change, then select Repair in the window that opens. Do the same for every Microsoft Visual C++ entry.

   

These steps were written for Windows 11 25H2 and 26H2, Windows 10 22H2. The full page with the other versions and what each result means: How to repair Microsoft Visual C++ Redistributable and .NET Framework

1. Repair the newest Microsoft Visual C++ v14 Redistributable (x64) entry, or its 2015-2022 form.
2. Repair the (x86) entry of the same version.
3. Restart the PC and test the program.

A missing vcruntime file has its own guide with Microsoft's download links: VCRUNTIME140_1.dll was not found. The Visual C++ package does not replace ucrtbase.dll on Windows 10 and 11, because Windows already has it.

Fix 6. ucrtbased.dll was not found: get a release build of the program

10 minutesNo riskThe message names ucrtbased.dll, with a d before the dot, as missing or not found.

ucrtbased.dll is the debug version of the runtime. Microsoft's library list marks it as not redistributable, so only a debug build of a program needs it, and only PCs with developer tools have it.

1. Note which program shows the message and where you got it.
2. Download the normal release version from the program's official site or store. A finished program should not ask for ucrtbased.dll.
3. If the program came from a friend, a course or a forum, ask its author for a release build.
4. If you build the program yourself in Visual Studio, switch the configuration from Debug to Release and build again.
5. Run the release build on the PC that showed the error.

Fix 7. Undo a recent change with System Restore

20 to 30 minutesLow riskCrashes started on a known day after a driver, Windows update or program was installed, and a restore point exists from before.

If the crash began right after a change to the system, returning system files, drivers and installed programs to that earlier state removes the change without guessing which one it was.

1. Open System Restore. Press Windows+R, type the command below and press Enter. You can also open Control Panel > Recovery > Open System Restore. If a first page opens, select Next.

   rstrui.exe

2. Choose a restore point. Select a restore point from a time before the problem started. The Description often names the event, such as a driver or app install. If the one you need is missing, select Show more restore points (shown only when there are more).

   

3. See what will change. Select Scan for affected programs. The upper list shows programs and drivers that will be removed; the lower list shows those that might come back and may need to be reinstalled. Select Close.

   

4. Start the restore. Select Next, check the summary and select Finish. Windows restarts and applies the restore point. Do not turn the PC off.
5. Check the result. After sign-in Windows reports whether the restore succeeded. Check whether the problem is gone.

These steps were written for Windows 11 and Windows 10 (the steps are the same). The full page with the other versions and what each result means: Undo recent changes with System Restore

1. Pick the newest restore point dated before the first crash.
2. Select Scan for affected programs and note what will be removed, so you can reinstall it later.
3. Finish the wizard, let the PC restart and test the program.

If the ucrtbase.dll crash is still there: what to check and what to send

When one program keeps crashing after all seven fixes, the cause is almost certainly in that program, and only its maker can fix it. Your job is to give them a complete report.

• What to send to the program's support: the full Event Viewer record from Fix 1 (copy it with Copy > Copy Details as Text), the program version, your Windows version and edition, and what you did right before the crash.
• A crash dump if they ask: Windows Error Reporting keeps reports that Reliability Monitor can show under View technical details. Send only what the vendor asks for.
• When it is likely hardware: many different programs crash at random, the faulting module changes between crashes, or blue screens appear too. Test the memory: How to test your RAM with Windows Memory Diagnostic, and check the disk: Check a disk for errors (chkdsk).
• When it is not this error any more: a record with another faulting module, or a box naming a different DLL, is a new problem with its own cause.

How to keep ucrtbase.dll crashes from coming back

If a program you build yourself crashes in ucrtbase.dll, run it under the Visual Studio debugger in a Debug configuration. The debug runtime, ucrtbased.dll, checks parameters and reports the exact call that failed, which the release crash record cannot show.

Frequently asked questions

What is ucrtbase.dll?

It is the Universal C Runtime, the library of standard C functions that programs built with Visual Studio 2015 or later use. Microsoft describes it as a Windows operating system component that is part of Windows 10 and later and Windows Server 2016 and later. The 64-bit copy is in C:\Windows\System32 and the 32-bit copy in C:\Windows\SysWOW64. It is not a virus and not part of any single program. Its version follows your Windows build and changes with Windows updates.

Why does ucrtbase.dll keep crashing my game?

In most cases the game crashes, not the DLL. The game passed bad data to a runtime function or detected corrupted memory, and the stop happened inside ucrtbase.dll. With exception code 0xc0000409 the process ended itself because its state was considered corrupted. Update the game, verify its files, start it once without mods and check the vendor's known issues. If other games and programs crash too, install Windows updates and run SFC and DISM.

What does faulting module name ucrtbase.dll mean?

It is a line in the Application Error record in Event Viewer. It names the module that was running when the program crashed. For ucrtbase.dll that means the crash happened in Windows' C runtime while it worked for the program. The line above it, the faulting application name, tells you which program to repair. The exception code and the faulting module path below it tell you the kind of crash and whether the system copy of the file was used.

Where can I download ucrtbase.dll?

You do not need to, and you should not. On Windows 10 and 11 the file is part of Windows. Microsoft's deployment documentation says the copy in the system directory is always used, even when a program brings its own copy. A file from a DLL site therefore does not change the crash and may carry malware. If the system copy is damaged, SFC and DISM restore it, and Windows Update brings the current version. Developers find redistributable copies for older Windows in the Windows SDK.

What is ucrtbased.dll and why is it not found?

ucrtbased.dll is the debug version of the Universal C Runtime. Microsoft's list of runtime library files marks it as not redistributable, so it exists only on PCs with Visual Studio or the Windows SDK. A program that asks for it was built in a Debug configuration and was not meant to be shared. Get the release version from the program's maker, or, if you are the developer, build a Release configuration. Copying the debug file to another PC is not allowed.

Does the ucrtbase.dll crash happen on Windows 11?

Yes, in the same way as on Windows 10. Windows 11 also includes the Universal CRT as part of the system, in the same folders. The record, the causes and the fixes are the same. On Windows 11 the runtime version follows the Windows 11 build, so installing all cumulative updates keeps it current. If a crash began right after a feature update to a new Windows 11 version, check whether the program's maker has released an update for that version.

Can I fix ucrtbase.dll with regsvr32?

No. The earlier version of this guide suggested regsvr32 ucrtbase.dll, but the command is meant for components that programs find through the registry. Microsoft describes ucrtbase.dll as an operating system component that Windows loads from the system directory, so registering it changes nothing. Use Windows Update and SFC and DISM to repair the runtime itself, and repair the crashing program.

Will reinstalling the Visual C++ Redistributable fix ucrtbase.dll?

Sometimes it helps, but not because of ucrtbase.dll itself. Microsoft explains that the Visual C++ Redistributable installs the Universal CRT only on PCs that do not have one, and Windows 10 and 11 always have one. A repair of the Visual C++ package fixes the program's vcruntime and msvcp libraries, which work together with the runtime. Try it when the crash report names those files too. For the runtime itself, Windows Update and SFC are the right tools.

Is a ucrtbase.dll crash a sign of a hardware problem?

Usually not. When one program always crashes in the same module, the cause is that program. Hardware becomes likely when many unrelated programs crash at random, the faulting module changes from crash to crash, or blue screens appear as well. Faulty memory corrupts data that any program may then pass to the runtime. In that case run Windows Memory Diagnostic and a disk check before you reinstall anything.