Data doesn't appear to have been stolen, but some customers should take some security precautions, wrote Brandon Fouts, general manager of Mandrill, which is a platform for managing transactional email that is owned by The Rocket Science Group.
"There's not evidence that any customer data was queried or exported, but unfortunately we can't completely rule out the possibility of access," Fouts wrote in a blog post.
Data that may have been exposed includes internal logs about emails sent, including sender and recipient addresses but not custom metadata or the content of messages, Fouts wrote.
The customers who may have been affected used Mandrill to send email between Feb. 6 and March 10 and used Mandrill's SMTP integration to send mail. Mandrill is contacting those believed to be at risk by email.
Customers who used Mandrill's SMTP integration should deactivate all API (application programming interface) keys and generate new ones as a precaution, Fouts wrote.
The attack came after Mandrill made a change to a firewall on Feb. 20 to allow more granular access to some of the company's servers.
"As a result, a cluster of servers hosting Mandrill's internal application logs was made publicly accessible instead of allowing internal-only access," Fouts wrote.
Mandrill discovered the vulnerability on March 10 after attackers unsuccessfully tried logging into those internal logging servers.
Log files on the affected servers have been backed up, and those servers won't be used anymore, Fouts wrote. SSH (Secure Shell) keys and Mandrill's API keys and passwords have been changed.
"We are deeply sorry for our error," Fouts wrote.
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