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GHSA-7jxj-rpx7-ph2c

LowCVSS 3.1 / 10
Published Jan 22, 2026·Last modified Feb 3, 2026
Affected Components(0)

No affected components available

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) =>
{
    var path = context.Request.Path.Value;

    if (!string.IsNullOrEmpty(path) && path.StartsWith("/media/forms/upload/", StringComparison.OrdinalIgnoreCase))
    {
        context.Response.OnStarting(() =>
        {
            context.Response.Headers["Cache-Control"] = "private, no-store, no-cache, must-revalidate";
            context.Response.Headers["Pragma"] = "no-cache";
            context.Response.Headers["Expires"] = "0";
            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.

Risk Scores
Base Score
3.1

The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information.

Threat Intelligence
2.9

Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.

EPSS
N/A

Probability that this vulnerability will be exploited in the wild within the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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Low severity
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