A backdoor has been discovered in the source code of a widely used FTP package.
Version 2.3.4 of the source code for vsftpd – billed as probably the most secure and fastest FTP server for Unix-like systems – was replaced with a compromised version with an invalid signature. The dodgy tarball version of the code was uploaded onto the main download site and available for around three days before the hack was detected by Chris Evans, the author of vsftpd, on Sunday (3 July).
Evans has moved the main download to a new site, https://security.appspot.com/vsftpd.html, which is hosted by Google App Engine. The counterfeit code was poorly disguised and it is unlikely that too many of the tech-savvy users of vsftpd fell victim to the hack. Nonetheless the incident illustrates that code repositories can be poisoned and the importance of checking digital signatures as a safeguard against falling victim to such shenanigans.
Evans reckons the whole incident is more likely the result of a prank than a serious attempt to compromise corporate file transfer facilities.
"The backdoor payload is interesting," Evans writes. "In response to a :) smiley face in the FTP username, a TCP callback shell is attempted. There is no obfuscation.
"More interestingly, there's no attempt to broadcast any notification of installation of the bad package. So it's unclear how victims would be identified; and also pretty much guaranteed that any major redistributor would notice the badness. Therefore, perhaps someone was just having some lulz instead of seriously trying to cause trouble." ®