Prevention of sensitive data exposure through cached form fields
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Home/Error");
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
});
}
The above code is a typical configuration for an ASP.NET Core application. It sets up various middleware components for handling HTTP requests.
However, this code does not include any measures to prevent caching of form fields. This means that if a user fills out a form in the application, the data they enter could be stored in the browser's cache. This could potentially expose sensitive data to anyone who has access to the user's browser.
The vulnerability lies in the fact that the application does not instruct the browser not to cache sensitive data. This could be a problem if, for example, the form is used to collect payment information or other sensitive data.
In the code, there is no use of
app.UseResponseCaching() or any other middleware that could prevent caching on the client side. Even though the application might use HTTPS for secure transmission of data, the data could still be cached on the client side if the application does not take measures to prevent this.
The lack of caching prevention could lead to a potential data leak on the client side, which might be exploited by an attacker with access to the client's browser.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Home/Error");
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.Use((context, next) =>
{
context.Response.GetTypedHeaders().CacheControl = new CacheControlHeaderValue()
{
NoStore = true,
NoCache = true,
MustRevalidate = true,
Private = true
};
context.Response.Headers[HeaderNames.Pragma] = "no-cache";
return next();
});
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
});
}
The above code fixes the vulnerability by setting appropriate cache-control headers to prevent caching of sensitive data.
The
app.Use middleware is used to set the
CacheControl header of the response. The
NoStore option is set to
true to prevent the browser and all intermediate caches from storing any version of the returned response. The
NoCache option is also set to
true to indicate that the returned response can't be used to satisfy a subsequent request to the same URL without first checking with the server if the response has changed. The
MustRevalidate option is set to
true to indicate that once the resource becomes stale, caches must not use their stale copy without successful validation on the origin server. The
Private option is set to
true to indicate that the response message is intended for a single user and must not be cached by a shared cache.
The
Pragma header is also set to
no-cache to include older HTTP 1.0 caches that do not understand the
Cache-Control header.
This way, the application ensures that sensitive data from form fields is not cached, thus mitigating the risk of information leakage.