Umbraco Forms version 4.0.0 up to and including 8.7.5 and below are vulnerable to a security flaw that could lead to a remote code execution attack and/or arbitrary file deletion. A vulnerability occurs because validation of the file extension is performed after the file has been stored in a temporary directory. By default, files are stored within the application directory structure at %BASEDIR%/APPDATA/TEMP/FileUploads/. Whilst access to this directory is restricted by the root web.config file, it is possible to override this restriction by uploading another specially crafted web.config file to the temporary directory. It is possible to exploit this flaw to upload a malicious script file to execute arbitrary code and system commands on the server.

Impact The 'Send email' workflow does not HTML encode the user-provided field values in the sent email message, making any form with this workflow configured vulnerable, as it allows sending the message from a trusted system and address (potentially bypassing spam and email client security systems).

Patches This issue affects all (supported) versions Umbraco Forms and is patched in 13.4.2 and 15.1.2.

Workarounds Unpatched or unsupported versions can workaround this issue by using the 'Send email with template (Razor)' workflow instead or writing a custom workflow type.

To avoid accidentally using the vulnerable workflow again, the SendEmail workflow type can be removed using the following composer (tested on Umbraco 10, 13, 14 and 15): c# using Umbraco.Cms.Core.Composing; using Umbraco.Forms.Core.Providers.Extensions; using Umbraco.Forms.Core.Providers.WorkflowTypes;

internal sealed class RemoveFormsSendEmailWorkflowTypeComposer : IComposer { public void Compose(IUmbracoBuilder builder) => builder.FormsWorkflows().Exclude<SendEmail>(); }