GHSA-7jxj-rpx7-ph2c Umbraco.Forms CDN may cache sensitive form uploads when processed by ImageSharp

Not scored Published 22 Jan 2026

Unauthenticated users can access sensitive form uploads via CDN cache poisoning when ImageSharp processes requests, requiring a CDN and specific file knowledge.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is GHSA-7jxj-rpx7-ph2c?

GHSA-7jxj-rpx7-ph2c is a vulnerability in Umbraco.Forms, published on 22 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Impact

Protected files uploaded through Umbraco Forms may be served to unauthenticated users when a CDN or caching layer is present and ImageSharp processes the request. ImageSharp sets aggressive cache headers by default, which can cause intermediary caches to store and serve files that should require authentication.

Patches

This issue affects all (supported) versions Umbraco Forms and is patched in 13.9.0, 16.4.0 and 17.1.0.

Workarounds

Add middleware to set cache headers for form uploads. Place the following code in your Startup.cs or Program.cs after app.UseStaticFiles() and any image processing middleware:

app.Use(async (context, next) =&gt;
{
    var path = context.Request.Path.Value;

    if (!string.IsNullOrEmpty(path) &amp;&amp; path.StartsWith(&#34;/media/forms/upload/&#34;, StringComparison.OrdinalIgnoreCase))
    {
        context.Response.OnStarting(() =&gt;
        {
            context.Response.Headers[&#34;Cache-Control&#34;] = &#34;private, no-store, no-cache, must-revalidate&#34;;
            context.Response.Headers[&#34;Pragma&#34;] = &#34;no-cache&#34;;
            context.Response.Headers[&#34;Expires&#34;] = &#34;0&#34;;
            return Task.CompletedTask;
        });
    }

    await next();
});

Alternatively, configure your CDN to bypass caching for URLs matching /media/forms/upload/*.

Note: The vulnerability requires:

A CDN in front of the website
An authenticated user having previously requested the image
Knowledge of the form GUID, entry GUID, and image filename

If no CDN is in use, this vulnerability does not apply.

Which versions are affected by GHSA-7jxj-rpx7-ph2c?

6 open source packages ship an affected version, including Umbraco.Forms.

Package	Affected	Fixed in
`Umbraco.Forms` NuGet	All versions	`13.9.0`
`Umbraco.Forms` NuGet	All versions	`13.9.0`
`Umbraco.Forms` NuGet	From `14.0.0-beta001`	`16.4.0`
`Umbraco.Forms` NuGet	From `14.0.0-beta001`	`16.4.0`
`Umbraco.Forms` NuGet	From `17.0.0-rc1`	`17.1.0`
`Umbraco.Forms` NuGet	From `17.0.0-rc1`	`17.1.0`

How do I fix GHSA-7jxj-rpx7-ph2c?

Upgrade Umbraco.Forms to a fixed version for your release line: 13.9.0, 16.4.0 or 17.1.0.

Is GHSA-7jxj-rpx7-ph2c being exploited?

There is no known exploitation of GHSA-7jxj-rpx7-ph2c in the wild and no public exploit code.