Why Can't I Set the Value of an HTML File Input to a Local File Path?

Setting Values for File Inputs in HTML

File inputs in HTML provide a convenient way for users to select files from their local file system. However, setting the value of a file input to a client-side disk file system path is not possible due to security considerations.

Imagine a scenario where you have a form with a file input:

<input type="file" />

If it were possible to set the input's value to a path on the client's file system, malicious websites could exploit this to gain access to sensitive data on the user's computer. For example, a website could create a form like this:

<form name="foo" method="post" enctype="multipart/form-data">
    <input type="file" value="c:/passwords.txt">
</form>
<script>document.foo.submit();</script>

Upon submitting the form, the website would be able to access the user's passwords.txt file. To prevent this security risk, browsers prohibit setting file input values to local file system paths.

The only way to set the value of a file input is to specify a publicly accessible web resource, as demonstrated in the following example:

<input type="file" value="https://example.com/image.png">

This technique is useful for displaying preview images or preselecting files that are already available online. However, it is not a substitute for allowing users to select files from their local file systems.

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