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Security alert · High

Mittwald hosting attacked via MCP server: admin services offline, customers should check

· 4 minutes read · Centoculus Security Team

Known since · attacks confirmed since

Affected: Customers of the web hoster Mittwald

What happened

On 12 November 2026, heise reported that the German web hoster Mittwald had been attacked through an MCP server. MCP (Model Context Protocol) servers connect tools and automation to other services and data. Mittwald is now in emergency mode. Its website runs in a limited mode, its blog is offline and the admin services for customers are switched off.

The report we have does not say how the attackers got in through the MCP server, which systems they reached, or whether customer data, websites or access credentials were affected. Treat any statement on these points as open until Mittwald confirms it.

Who is at risk

  • Agencies, companies and individuals who host websites, web shops or other services at Mittwald.
  • Their end customers, if access data or websites were exposed. This has not been confirmed so far.

If you do not host anything at Mittwald and do not connect to Mittwald services, this incident does not affect you directly.

What to do now

  1. Get information only from Mittwald's official channels. Expect phishing emails and calls that use the incident as cover. Do not enter credentials through links in unexpected messages, and do not give access data to callers.
  2. Do not make rushed changes while the admin services are offline. Write down which projects, domains and accounts you have at Mittwald so you can work through them quickly later.
  3. When access is back, change the passwords of your Mittwald customer accounts and turn on two-factor authentication where it is offered.
  4. Rotate other credentials that were stored at or used with Mittwald: API tokens, SSH keys, FTP/SFTP and database passwords, and mailbox passwords. Also change the passwords of CMS and shop admin accounts on sites hosted there.
  5. If you connected MCP servers, AI tools or other automation to your hosting accounts yourself, revoke their tokens and issue new ones with the fewest rights they need.
  6. Make sure you have a current backup of every site that you keep outside Mittwald. Do not overwrite older backups yet, because you may need a known good state.
  7. Tell your own customers what happened in plain terms, and pass on Mittwald's statements as they are published.

How to check whether you were hit

  • Once the admin services are back, review the account activity, the user and access lists, and the SSH keys and API tokens in your Mittwald accounts. Look for anything you did not create.
  • Compare the files of your websites with your own backups or your Git repositories. Look for new or changed PHP files, unknown admin users in your CMS or shop, and changed DNS records or mail forwarding.
  • Check the access and error logs of your sites from the days around 12 November 2026 for unusual logins or uploads.
  • Follow Mittwald's updates on which systems and data were affected. If Mittwald confirms that customer data or access credentials were exposed, consider your own data protection reporting duties.

Update November 14, 2026

Mittwald now says the attacker used a vulnerability in Mittwald's own MCP server, which lets customers connect the mStudio admin platform to AI assistants. Through it the attacker read session tokens and got into 56 customer projects. According to Mittwald, passwords were not read and all session tokens have been revoked. Affected customers are told by personal email. Reports say the attacker first probed the flaw on 21 October 2026, used it on 27 October and was found on 4 November. Mittwald blocked the MCP server, mStudio and SSH on 5 November, turned access back on later, and cut SSH, mStudio and the customer center again in the night of 12 November. Websites and mailboxes have stayed reachable. Mittwald says its own website was not taken over or defaced.

Sources

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