SynopsisThe remote Fedora host is missing a security update.
DescriptionJann Horn reported that there is a possible race condition in the handling of the MKD/XMKD FTP commands, when the UserOwner directive is involved, and the attacker is on the same physical machine as a running proftpd. This race applies to mod_sftp and the handling of the MKDIR SFTP request as well.
Note that using the DefaultRoot directive to restrict sessions mitigates this attack, since the symlinks created by the local attacker will point outside of the chroot(2) area within the FTP session, and thus the ownership change will fail. The default configuration in Fedora applies the DefaultRoot directive to all users except 'adm'.
The upstream reference for this issue is:
This update includes upstream's backport to proftpd 1.3.4 of the fix for this issue.
Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
SolutionUpdate the affected proftpd package.