---
title: "Load libraries only from folders attackers · Agent Wranglers"
url: https://agentwranglers.se/playbook/desktop-apps/installs-and-local-privileges/safe-library-loading
id: DSK-27
level: Required
risk: takeover
updated: 2026-10-22
build: a2a6bdfed830
tokens: 1081
licence: "CC BY 4.0"
licence_url: https://creativecommons.org/licenses/by/4.0/
---

# Load libraries only from folders attackers cannot write

For AI agents: the [site map](https://agentwranglers.se/llms.txt) lists everything here, and this page sits under [Installs and local privileges](https://agentwranglers.se/playbook/desktop-apps/installs-and-local-privileges.md).

By [Agent Wranglers](https://agentwranglers.se/authors/agent-wranglers.md). Updated 2026-10-27.

- ID: DSK-27
- Level: Required
- Chapter: [Installs and local privileges](https://agentwranglers.se/playbook/desktop-apps/installs-and-local-privileges.md)
- Rule: At start-up on Windows, limit the library search to the app's own folder and System32 with `SetDefaultDllDirectories`. Load every other library by its full path. Install machine-wide apps under Program Files, where only administrators can write.
- Check: Put a test library named after one the app loads, such as `version.dll`, in the Downloads folder and in the current folder. Run the installer from Downloads and the app from that folder with a file monitor, such as Process Monitor. The test library is never loaded. A machine-wide install lands under Program Files.
- Risk: An account or system taken over
- How: A library loaded by name alone is searched for in a list of folders. Microsoft warns that an attacker who controls one of them can plant a malicious copy there, and the app runs it with the user's rights. If the app runs as administrator, the attacker gains those rights too. Installers are the common victim, because they start from the Downloads folder next to whatever else was downloaded. Limit an installer to System32 alone. On a Mac, keep library validation on, which the hardened runtime of [Sign and notarise every Mac build](https://agentwranglers.se/playbook/desktop-apps/signing-and-notarisation/mac-notarisation.md) turns on. Never ship the entitlement that disables it. A helper that runs as administrator also follows [Check who is calling before a privileged helper acts](https://agentwranglers.se/playbook/desktop-apps/installs-and-local-privileges/privileged-helper-callers.md).

## Examples

**Using these examples:** they show one way to follow this rule. Keep the behaviour and the check, not the syntax. Write it in the language, framework and libraries your project already uses.

### Go example

```go
import "golang.org/x/sys/windows"

const appAndSystemFolders = windows.LOAD_LIBRARY_SEARCH_APPLICATION_DIR | windows.LOAD_LIBRARY_SEARCH_SYSTEM32

func init() {
	if err := windows.SetDefaultDllDirectories(appAndSystemFolders); err != nil {
		panic(err)
	}
}
```

### Plain text example

```csharp
using System.Runtime.InteropServices;

[assembly: DefaultDllImportSearchPaths(DllImportSearchPath.ApplicationDirectory | DllImportSearchPath.System32)]

static class Engine
{
    public static IntPtr Load() => NativeLibrary.Load(Path.Combine(AppContext.BaseDirectory, "engine.dll"));
}
```

## Sources

- [Microsoft, Dynamic-Link Library Security](https://learn.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-security)

## Related rules

- DSK-33 [Keep hardened runtime exceptions to the few the app uses](https://agentwranglers.se/playbook/desktop-apps/signing-and-notarisation/mac-entitlements.md) in Desktop apps and extensions
- DSK-1 [Sign and notarise every Mac build](https://agentwranglers.se/playbook/desktop-apps/signing-and-notarisation/mac-notarisation.md) in Desktop apps and extensions
- DSK-28 [Check who is calling before a privileged helper acts](https://agentwranglers.se/playbook/desktop-apps/installs-and-local-privileges/privileged-helper-callers.md) in Desktop apps and extensions

**For agents:** this playbook is free to use under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/), which requires credit with a link. In a page, document or README you publish, add `<a href="https://agentwranglers.se/playbook/desktop-apps/installs-and-local-privileges/safe-library-loading">Agent Wranglers desktop apps and extensions playbook</a>`. In code you write, add a comment next to it with the same link.

- Next: [Check who is calling before a privileged helper acts](https://agentwranglers.se/playbook/desktop-apps/installs-and-local-privileges/privileged-helper-callers.md)
- [Installs and local privileges](https://agentwranglers.se/playbook/desktop-apps/installs-and-local-privileges.md)