If you’re a Firefox user, you should update your browser immediately. Mozilla was informed earlier this week by an astute Firefox user that a Russian news site was was using malicious advertisements to take advantage of an exploit in the browser when installed on Windows and Linux machines.
The exploit takes advantage of a vulnerability in the PDF viewer that is built into the Firefox browser. That also means that the mobile version of Firefox, which doesn’t include the PDF viewer, is not affected. Mac users were also spared from this particular exploit, but Mozilla still suggests that they upgrade Firefox to combat against future mutations of the exploit.
But for affected versions of Firefox, malicious parties were able to sniff out “sensitive files” on your computer and upload them to a Ukrainian sever. Mozilla describes the modus operandi of the exploit, stating:
On Windows the exploit looked for subversion, s3browser, and Filezilla configurations files, .purple and Psi+ account information, and site configuration files from eight different popular FTP clients. On Linux the exploit goes after the usual global configuration files like /etc/passwd, and then in all the user directories it can access it looks for .bash_history, .mysql_history, .pgsql_history, .ssh configuration files and keys, configuration files for remina, Filezilla, and Psi+, text files with “pass” and “access” in the names, and any shell scripts.
The most interesting part about this whole exploit is that it leaves no trace of its existence on your machine, so you would never know if you were the victim of these data vampires. As a result, Mozilla is asking users to “change any passwords and keys found in the above-mentioned files if you use the associated programs.”
Interestingly enough, Mozilla also says that Firefox users with adblocking software installed were likely protected from the exploit. Regardless of whether you’re a Mac user or use adblocking software, you should still upgrade to Firefox 39.0.3 to be fully protected in the future.
Mozilla was in the news last week when its CEO blasted Microsoft for taking it upon itself to seemingly make Edge the default browser in Windows 10 when upgrading, and making it slightly more difficult to revert back to the previously default browser. Unfortunately for Mozilla, most people were unsympathetic to its outrage and Microsoft of course didn’t issue a response (not that we expected them to).