PuTTY Not Working on Windows 11: How to Fix It

What's causing this error

There is no single "PuTTY doesn't work on Windows 11" bug. PuTTY is actively maintained and fully compatible with Windows 11, including 24H2 and Arm machines. When it misbehaves, the cause is one of four things: the installer can't run, Windows is blocking the program, a specific connection error is appearing, or a display or settings quirk makes it look broken.

Match what you're seeing:

If your PuTTY window opens and the problem is a specific error dialog, the exact wording of that dialog is the diagnosis. Use the matching page above; the rest of this page covers everything that goes wrong outside a connection.

How to fix it

Installer fails with error 2503 or 2502

The installer has encountered an unexpected error ... 2503 (or 2502) is a Windows Installer permissions problem, not a PuTTY problem: the MSI was started without the elevation it needs to write to the temp folder. Double-clicking the file in Downloads is exactly the path that triggers it.

Run the installer from an elevated prompt instead. Right-click Start, choose Terminal (Admin), then:

cd $env:USERPROFILE\Downloads
msiexec /i putty-64bit-0.85-installer.msi

The installer then runs normally. Adjust the filename if you downloaded the 32-bit or Arm64 build.

Windows blocks the download or first run

Two separate guards can fire here:

• The browser flags the download as "not commonly downloaded". Choose Keep (in Edge: three dots on the download > Keep > Show more > Keep anyway).
• SmartScreen shows "Windows protected your PC" on first run. Click More info, then Run anyway.

Only click through after confirming you have the genuine installer. Our PuTTY download page lists the official builds with their SHA-256 checksums; compare with:

Get-FileHash $env:USERPROFILE\Downloads\putty-64bit-0.85-installer.msi

If the hash doesn't match, delete the file and download again from the official source. A mismatched hash is the one case where the warning deserved your attention.

Firewall or antivirus is blocking putty.exe

If every connection times out, even to servers you can reach from other machines, and the sibling pages above don't apply, something on your PC is eating the traffic:

1. Windows Defender Firewall: Windows Security > Firewall & network protection > Allow an app through firewall. Check whether putty.exe is listed and allowed on your current network profile. Outbound traffic is allowed by default, so also check for third-party firewall rules.
2. Antivirus quarantine: some AV products flag old PuTTY builds (real vulnerabilities were fixed in recent versions) or block unsigned copies downloaded from mirror sites. Check the AV's quarantine log. The fix is a current official build, not an AV exclusion for an old binary.
3. Corporate machines: VPN clients and SSL-inspection proxies commonly block outbound port 22. Test on another network (phone hotspot) to confirm; if that works, it's a policy conversation, not a PuTTY setting.

Blurry text on a high-DPI display

On 4K and high-DPI laptop screens Windows scales PuTTY's window by stretching it, which blurs the terminal font. Fix it per executable:

1. Right-click putty.exe (or the Start Menu shortcut > Open file location > right-click) and choose Properties.
2. Compatibility tab > Change high DPI settings.
3. Tick Override high DPI scaling behavior and set it to System (Enhanced).

Then pick a larger font for readability: Window > Appearance > Font, something like Consolas 12.

Saved sessions missing after a reinstall

PuTTY stores sessions in the registry under HKCU\Software\SimonTatham, not in files, so they are not deleted by uninstalling or reinstalling PuTTY. If sessions look gone, you're on a new Windows install, a new machine, or a different user account.

Back them up and move them like this:

# On the old machine / account:
reg export HKCU\Software\SimonTatham putty-sessions.reg

# Copy the .reg file over, then on the new machine:
reg import putty-sessions.reg

Do the export before wiping a machine; there is no way to recover sessions from an installer or a Downloads folder afterwards.

Arm laptops: use the Arm64 build

On Snapdragon-based Windows 11 machines (Surface Pro 11, Snapdragon X laptops) the standard 64-bit x86 build runs through emulation. It works, but the native Arm64 build starts faster and uses less battery. Get putty-arm64-0.85-installer.msi from the download page.

Common edge cases