Email hosting provider Cock.li in Germany has confirmed it suffered a data breach after threat actors exploited its Roundcube platform. This significant security incident exposed all users who had logged in to the popular mail service since the year 2016. An estimated 1,023,800 people were affected by this breach, along with contact entries for an additional 93,000 other users. Cock.li is a privacy-focused free email hosting provider with lax moderation policies, run by a single operator since the year 2013. The service is popular among people who distrust major providers and also members of the information security and open-source communities.
Late last week, the Cock.li email service was unexpectedly disrupted without any public explanation, leaving many users wondering what had happened.
Soon after the outage began, a threat actor claimed to be selling two databases that were dumped from Cock.li’s systems. These databases contained sensitive user information, which was offered for sale for a minimum price of one Bitcoin, or $92,500. Cock.li later published an official statement on its website yesterday, confirming the data breach and the validity of the threat actor’s claims. The exposed information includes email addresses, first and last login timestamps, failed login attempts, and various Roundcube software settings and preferences.
The email service’s official announcement clarifies that user account passwords and the content of emails were not compromised in this breach. Additionally, the IP addresses of the users were not exposed, as this information is not present in the stolen databases. Meanwhile, the 10,400 account holders who had some of their third-party contact information exposed will be getting a separate notification. For everyone who has used the popular email service since 2016, it is strongly recommended that they reset their account passwords.
This data breach could be valuable to researchers and law enforcement, as the exposed information can be used to learn about threat actors.
The operator of Cock.li says they believe the data was stolen using an old RoundCube SQL injection vulnerability, CVE-2021-44026. This breach comes just as the service recently analyzed another critical remote code execution flaw in Roundcube, which is actively exploited. Their detailed analysis led them to permanently remove the Roundcube webmail software from their platform in June of the year 2025. The announcement mentions that better security practices could have prevented this user data leak, admitting they should not have been running Roundcube. Those who want to continue using Cock.li for email will now have to use an IMAP or SMTP/POP3 client to access their accounts.
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