> Vulnerability in 4.4BSD Secure Levels Implementation > This vulnerability is significant in that it allows an intruder to > covertly modify running processes. The correct behaviour is to make > the address space of these processes immutable. Although an intruder > can still kill them and start others in their place, the death of system > daemons will (should) draw attention on secure systems. The key word is "should" draw attention. Unless there is an application (or the system itself) that periodically checks for any change in status of a system daemon (like the change of a PID), I suspect that most sysadmins will not even notice that a system daemon has died and restarted. To help plug this vulnerability one of the following options might be desirable, 1. Disallow sending signals to processes started from immutable binaries, except from init, e.g. during shutdown. Advantage: Improved security. Disadvantages: Administration may be virtually impossible and may break existing applicaitons. 1a. A variation of #1 except using a new "unkillable" flag which denotes immutable binaries that cannot be sent signals. Advantage: May break fewer applications than #1. 2. Have init manage critical system daemons via /etc/ttys. When a critical daemon dies, automatically restart a new one. Advantage: Administratively more palatable. Disadvantage: Race condition possible to replace a system daemon with a rogue daemon. 3. Replicate the immutable flag when a file is copied. Advantage: Some improved security. Disadvantage: Intruder can FTP a rogue daemon and run it instead. Regards, Phone: (250)387-8437 Cy Schubert Fax: (250)387-5766 Open Systems Group Internet: cschuberat_private ITSD Cy.Schubertat_private Government of BC
This archive was generated by hypermail 2b30 : Fri Apr 13 2001 - 13:57:39 PDT