Yesterday was the data protection day in Europe[1]. I was not on duty so I’m writing this quick diary a bit late. Back in 2020, the Nitro PDF service suffered from a data breach that impacted many companies around the world. This popular service allows you to create, edit and sign PDF documents. A few days ago, the database leak was released in the wild[2]:  14GB compressed, 77M credentials.

I had this opportunity to have a look at the data and it provides really interesting information. The archive contains dumps of SQL tables from a relational database. We have a file with the users' data. The classic email addresses and passwords (hopefully hashed) are present but also a user ID. A second file is the dump of a SQL table containing information about documents processed with Nitro PDF. Because it’s a relational database, we can use the user's ID to find who worked on which document(s) and when (because timestamps are also present). The information you have about documents is the title and a thumbnail reference (but not available hopefully). Example:

114193114       2013-10-28 21:46:21.765 2013-10-28 21:46:22.62  f       5430610411990818132     f       nitrocloud-prod|437b88f9-3f81-4952-9ec4-
97d8524a890e    Concept Note    \N      f       f       \N      114193118       \N

"114193114" is the user ID, "Concept Note" is the document title.

I did some correlation searches for my customers and I was able to match which user was working on a specific document at a specific time.

From a broader point of view, can we guess the type of data that was exchanged via this cloud service? I extracted all the document titles, performed some cleanup, and extracted a word list to generate this word cloud:

As you can see, many words look "juicy" and are directly related to business activities! By linking document titles with email addresses we learn about potential victims who could be interesting targets for social engineering or phishing attacks! 

Always be aware that cloud services store a lot of information that you don't really want to see out of your perimeter!

[1] https://www.coe.int/en/web/portal/28-january-data-protection-day
[2] https://www.bleepingcomputer.com/news/security/hacker-leaks-full-database-of-77-million-nitro-pdf-user-records/

Xavier Mertens (@xme)
Senior ISC Handler - Freelance Cyber Security Consultant
PGP Key