GNU finger Privilege Dropping Vulnerabilities

There are two vulnerabilities in the GNU finger package downloadable from metalab that have to do with proper privilege dropping. The finger daemon runs as root by default and responds to finger queries for information on the system's users. The first vulnerability allows a malicious user to have an arbitrary program run with gid 0 if the use of .fingerrc is permitted. This is because fingerd drops the uid (0) before gid, leaving itself lacking the permission to drop the gid. The second vulnerability allows an attacker to create a symbolic link from .plan, .forward or .project that fingerd will follow and read with uid 0 (ie. .plan -> /etc/shadow). These vulnerabilities are not new, they were exposed in 1995 on BugTraq and remain unfixed to this day.


 

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