https://www.vice.com/en_us/article/qjpgyp/bug-in-macs-default-text-app-could-let-hackers-reveal-your-ip-address

TextEdit, the humble text editing app that's pre-installed on Macs, could have revealed your IP address to a hacker. 

Paulos Yibelo found a bug that potentially allowed a hacker to trick a victim's Mac into revealing their IP address just by downloading a .txt file and opening it with TextEdit. The issue was that TextEdit automatically parsed and interpreted HTML code. To trigger this vulnerability, the hacker would have simply needed to insert some malicious HTML code into the text file to make TextEdit ping a remote server controlled by the hacker, as the researcher explained in a blog post.